North Korea has been warned it faces "total annihilation" after Kim Jong-un tested a nuclear bomb with the power to kill millions of people.
US Defense Secretary Jim Mattis vowed to meet any threat to America with 'a massive military response'.
And South Korea also responded with a live-fire simulation of an attack on the dumpy despot's test site.
The live-fire exercise saw rockets launched from F-15 fighter jets and ballistic missiles from the ground.
It came as South Korea's military chiefs reportedly detected preparations for yet another North Korean long-range missile test.
Chang Kyung-soo, an official from South Korea's Defense Ministry, told lawmakers that Seoul had seen evidence of a future North Korean ICBM launch to show off its claimed ability to target the US.
But he did not give any details about when the launch is expected to take place, according to KBS News.
The US and South Korea are now set to deploy a nuclear-powered aircraft carrier and strategic bomber in response to the latest tests, Yonhap News agency reported.
South Korea also hit back with a live-fire simulation of an attack on Kim Jong-un's test site.
Seoul's Joint Chiefs of Staff (JCS) said the released live weapons "accurately struck" a target in the sea off the country's eastern coast.
North Korea conducted its sixth and most powerful test of a hydrogen bomb on Sunday night.
South Korean military chiefs believe the explosive power of the bomb is around 50 kilotons – some 50 less than previously estimated.
The test triggered an 6.3-magnitude artificial quake – ten times larger than any of North Korea's previous attempts.
It was seen as a direct challenge to Trump, who has vowed to stop North Korea developing nuclear weapons that could threaten the United States.
Hours after the rest, the White House warned North Korea of "total annihilation" after Kim Jong-un detonated a new thermonuclear bomb.
The test was seen as a direct challenge to Trump, who has vowed to stop North Korea developing nuclear weapons that could threaten the United States.
US Defense Secretary Jim Mattis said Trump asked to be briefed on all available military options.
Mattis said: "Any threat to the United States or its territories, including Guam or our allies will be met with a massive military response, a response both effective and overwhelming.
"We are not looking to the total annihilation of a country, namely North Korea. But as I said, we have many options to do so."
Trump also refused to rule out a US attack on North Korea after the rouge nation issued a "severe warning" to America.
The Korean Central News Agency said: "If the US imperialists awkwardly provoke the DPRK, they would not be able to escape from the greatest disaster."
When questioned if he would attack North Korea, Trump said: "We'll see".
The president also tweeted to say that the US was considering cutting economic ties with any countries that do business with North Korea.
While the US has virtually no trade with the North, the burden of sanctions as described by Trump would fall heavily on China, which buys about 90 per cent of North Korean exports.
North Korea has conducted a major Nuclear Test. Their words and actions continue to be very hostile and dangerous to the United States…..
— Donald J. Trump (@realDonaldTrump) September 3, 2017
..North Korea is a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success.
— Donald J. Trump (@realDonaldTrump) September 3, 2017
South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!
— Donald J. Trump (@realDonaldTrump) September 3, 2017
Hours after the test, US President took to Twitter, writing: "North Korea has conducted a major Nuclear Test. Their words and actions continue to be very hostile and dangerous to the United States.
"North Korea is a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success."
He then added: "South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!"
North Korea this morning confirmed on state media they had conducted a hydrogen bomb test, saying it was a "perfect success", and adding the H-bomb can be loaded onto an intercontinental missile.
World leaders have been quick to condemn North Korea's test, calling on the United Nations Security Council to react to the violation.
South Korean President Moon Jae-In has called for the "strongest punishment" against North Korea.
Presidential security adviser Chung Eui-Yong said after an emergency National Security Council meeting that Moon had called for "all diplomatic measures including UNSC sanctions resolutions to completely isolate North Korea".
French President Emmanuel Macron urged the United Nations Security Council to react quickly and decisively.
He said: "The international community must treat this new provocation with the utmost firmness, in order to bring North Korea to come back unconditionally to the path of dialogue and to proceed to the complete, verifiable and irreversible dismantling of its nuclear and ballistic programme."
China, the only North Korean ally that is a permanent member of the Security Council, urged its neighbour to stop "wrong" actions that worsen the situation.
It said it would fully enforce UN resolutions on the country.
Foreign Secretary Boris Johnson said called the test "reckless", saying: "It's our view in the UK overwhelmingly that peaceful diplomatic solutions are best. We really don't see an easy military solution – the distance between North Korea and Seoul is very small.
"Much more productive is to continue the international diplomatic effort.
"What the Chinese always say is there's a kind of equivalence between the South Korean/US exercises and nuclear exercises carried out by North Korea. We don't accept that.
"Our message to the Chinese is that we think there's more scope for you to put economic pressure on the North Koreans."
The Russian foreign ministry called for calm, saying: "In the emerging conditions it is absolutely essential to keep cool, refrain from any actions that could lead to a further escalation of tensions."
Australian Prime Minister Malcolm Turnbull also condemned the "flagrant defiance" of the United Nations Security Council resolution, saying: "North Korea's reckless conduct poses a grave danger to global peace and security."
The Korea Meteorological Administration initially reported "an artificial tremor" at 12:36 p.m local time in the North Hamgyeong Province, from a site used for nuclear testing by the North Korean regime.
The US Geological Survey and Chinese authorities both confirmed the tremor, with South Korea's weather agency later revising the artificial quake to 5.7-magnitude.
North Korea's previous nuclear tests caused tremors just over 5 on the Richter scale – one tenth the magnitude of the current test – suggesting the device being tested this time was significantly more powerful.
Hours before the tremor Kim Jong-un was pictured inspecting nuclear weapons, and North Korea released a statement saying he had seen a new "thermonuclear" warhead being loaded onto an ICBM.
The country bragged the new weapons had "great destructive power" and have a yield that is adjustable from "tens to hundreds of kilotons" and can be detonated at high altitudes.
That would put it in the same bracket as missiles currently in use by the UK and US, though significantly less than US missiles had at their peak before weapons-reduction treaties with Russia dramatically reduced payloads.
What's the difference between a hydrogen bomb and an atomic bomb?
A HYDROGEN bomb is far more powerful than conventional atomic weapons.
While A-bombs use nuclear fission to create an explosion, the H-bomb gets an extra boost of nuclear fusion — the process that powers our sun. One would wipe out all life in a two-mile radius, obliterating a city the size of Leeds or Cardiff in a flash.
The main problem is making the device small enough to fit inside a missile warhead.
Kim's regime has also boasted that it can build as many nuclear weapons as it wants.
North Korea sharply increased regional tension this week with the launch of its Hwasong-12 intermediate-range ballistic missile that flew over Japan and landed in the Pacific.
Japanese PM Shinzo Abe said that if the country had indeed tested a nuclear device this would be "absolutely unacceptable".
The country lodged an official protest through North Korea's embassy in Beijing.
The state was reported to have been working to develop a nuclear-tipped missile capable of hitting the United States and has recently threatened to land missiles near the US Pacific territory of Guam.
The August provocation followed test launches of two long-range ballistic missiles in July that suggested a range of 10,000km or more – which would put many parts of the US mainland within striking distance of the tubby tyrant.
Earlier this week North Korean soldiers were being urged to steal food in preparation for an all-out war with the might of the US.
Military officers are turning a “blind eye” to the looting, and are even said to be encouraging it as a means of keeping up their strength because of meagre army rations.
“The military officers are instructing their soldiers, exhausted after training, to eat corn in the fields because war is imminent," a source told news outlet Daily NK.
Mad rulers' 11 years of nuke tests
OCTOBER, 2006: Kim Jong-il carries out North Korea’s first nuke blast, a 1-kiloton explosion with a 4.2 magnitude tremor.
MAY, 2009: Second blast of between 2-8 kilotons.
FEBRUARY, 2013: Kim Jong-un conducts his first test, a “miniaturised and lighter nuclear device with greater explosive force”.
JANUARY, 2016: Claims a 4-6 kiloton bomb has been exploded, with 5.1 magnitude earthquake.
SEPTEMBER, 2016: Seismic activity after blast near Punggye-ri underground nuclear test site.
SEPTEMBER, 2017: A 6.3 magnitude quake detected after suspected 120-kiloton H-bomb detonated.
“They are even threatening their soldiers, saying ‘If you become malnourished despite permission to eat the corn, you will face difficulties.’”
Another source from Ryanggang Province, claimed: “Soldiers carrying big sacks of unripened corn can be frequently seen at the markets. They see the corn at cheap prices to merchants who have made deals in advance.”
The order is said to have come direct from the "Glorious Leader" – who is said to thrive on a diet of fine wines and continental cheeses.
In response, fed-up farmers have set up guard posts in an attempt to protect their crops.
Hit on city would kill 4 million
IF the North Koreans have a hydrogen bomb then this is a game-changer — 120 kilotons is big for a weapon.
Something that size would wipe out anything at least in a two-mile radius.
It doesn’t bear thinking about but the fireball and immediate radiation heat would burn everything in that radius.
Then you get a huge blast wave that knocks over buildings and wipes out everything in its path.
If a bomb of that size was dropped on Tokyo or Seoul it would kill three or four million people.
The deaths from radiation fallout would be secondary as most destruction would be huge.
The typical conventional fission-only nuclear weapons are somewhere in the order of ten kilotons.
More than 100 kilotons is either a huge amount of material — or it is a hydrogen bomb which has this sort of power.
It is a big step-up to have a hydrogen weapon. They are very devastating.
By Prof Paddy Regan, nuclear physics expert
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