Donald Trump has made his strongest threat yet against North Korea, vowing to "totally destroy" the country if it attacks the US or its allies.

In a wideranging speech to the United Nations General Assembly in New York overnight, the US President repeated his mocking nickname for Kim Jong-un - "Rocket Man" - and slammed his leadership as a "depraved regime".

"The United States has great strength and patience, but if it is forced to defend itself or its allies, we will have no choice but to totally destroy North Korea," he said.

"Rocket Man is on a suicide mission for himself and for his regime.

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"The United States is ready, willing and able, but hopefully this will not be necessary."

In a dark and forceful 40-minute address that identified rogue regimes as the "scourge of our planet today", Trump reserved his strongest condemnation for the hermit kingdom.

Three chairs sit empty in the spot reserved for the North Korean delegation as Trump speaks to the United Nations General Assembly. Photo / AP
Three chairs sit empty in the spot reserved for the North Korean delegation as Trump speaks to the United Nations General Assembly. Photo / AP

"No one has shown more contempt for other nations and for the wellbeing of their own people than the depraved regime in North Korea," he said, without ever referring to Kim by name.

"It is responsible for the starvation deaths of millions of North Koreans and for the imprisonment, torture, killing and oppression of countless more."

The President pointed to the death of American university student Otto Warmbier, the assassination of Kim's brother and the enslavement of a 13-year-old Japanese girl as proof of the regime's wickedness.

"If this is not twisted enough, now North Korea's reckless pursuit of nuclear weapons and ballistic missiles threatens the entire world with unthinkable loss of human life," he said.

"It is an outrage that some nations would not only trade with such a regime but would arm, supply and financially support a country that imperils the world with nuclear conflict."

He added: "It is time for North Korea to realise that the denuclearisation is its only acceptable future."

Trump thanked China and Russia for signing on to two sets of UN Security Council sanctions against North Korea, but said "we must do much more".

"It is time for all nations to work together to isolate the Kim regime until it ceases its hostile behaviour," he said.

Trump implored the UN members to "confront together those who threaten us with chaos, turmoil and terror" - such as North Korea, Iran and Syria.

"They respect neither their own citizens nor the sovereign rights of their countries," he said.

"If the righteous many do not confront the wicked few then evil will triumph.

"When decent people and nations become bystanders to history, the forces of destruction only gather power and strength."

'NAILED IT'

New York based Asian affairs expert Sean King told news.com.au with all Rocket Man apologies to Elton John, the President "nailed it".

However King said he wished Trump had mentioned the Americans currently being held in North Korea.

He also criticised the President for thanking China, as "Beijing's an obstacle to progress on this issue."

Overall King believes Trump was strong in his message.

"I give him an A for the Korea portion of his UN General Assembly speech today," he said.

King said sanctioning the mainland Chinese entities and banks that enable North Korea's weapons programs is the key and Trump "has at least identified the real issues and called out the Kim regime for the international crime syndicate it is".

He also said those outraged at Trump's threats to destroy North Korea should remember one thing.

"He only raised that potential course of action in the event of a North Korean attack on us and or our allies," he said.

Israeli Prime Minister Benjamin Netanyahu called the speech the most powerful UN speech he's heard in 30 years.

Israel has long been a vocal critic of Iran and views its nuclear weapons program as a major threat.

However not everyone was so praiseworthy of the President.

US Democrat Senator Dianne Feinstein said the UN was a place for the promotion of peace yet the President had used it to threaten war.

Nuclear disarmament campaigner John Hallam said Trump's speech took the Korean crisis to a whole new level, calling his remarks irresponsible, destabilising and dangerous.

"It has made it much, much less easy to bring that conflict to a peaceful resolution, and much, much more likely that there will indeed be conflict between the US and the DPRK, and that such a conflict would become nuclear very quickly," Hallam said.

He also said the remarks made it more probable that the DPRK (Democratic People's Republic of Korea) would feel more backed into a corner and therefore more likely to launch pre-emptive action against the US.

"While the DPRK regime is certainly not suicidal, Kim Jong-un may after this speech feel he has no alternative but to attack the US before the US attacks him, doing as much real damage as he can," Hallam said.

Speaking on Sunrise this morning Prime Minister Malcolm Turnbull said Trump's words were strong.

However he said the reality was if North Korea attacked the US or its allies it would be a suicide mission for the regime.

When asked by host David Koch what his gut feeling was, Turnbull said: "I don't think this guy would commit suicide because that's the truth."

"The reality is if North Korea decides to attack the US or its allies ... there will be a massive response that will end the regime."

When asked if Trump's words and name calling inflamed the situation, Turnbull said the President was simply stating the reality of the situation.

TRUMP CALLS FOR 'GREAT REAWAKENING'

Before Trump's Tuesday speech, the White House promised that it would be a "deeply philosophical" address. The philosophy that Trump encouraged UN members to embrace was that patriotism, democracy and the people each nation serves should be central to leaders' decision-making.

"We are calling for a great reawakening of nations, for the revival of their spirits, their pride, their people and their patriotism," he said towards the end of his speech.

"History is asking us whether we are up to the task. Our answer will be a renewal of will, a rediscovery of resolve and a rebirth of devotion.

"We need to defeat the enemies of humanity and unlock the potential of life itself."

Touching upon a booming US stock market, a recovering Europe, a diminished middle class and the threat of terrorism, Trump's speech bounced between the two poles of hope and horror.

"We meet at a time of both immense promise and great peril," he said.

"It is entirely up to us whether we lift the world up to new heights or let it fall into a valley of disrepair."

He encouraged other nations to follow his "America first" doctrine and put their own interests first.

"We do not expect diverse countries to share the same cultures, traditions or even systems of government, but we do expect all nations to uphold these two core sovereign duties: to respect the interests of their own people and the rights of every other sovereign nation," he said.

Members of the Iranian delegation listen as Trump speaks. Photo / AP
Members of the Iranian delegation listen as Trump speaks. Photo / AP

DEAL AN 'EMBARRASSMENT' TO US

Trump also took direct aim at the "reckless regime" and "corrupt dictatorship" of Iran, which he said "speaks openly of mass murder, vowing death to America, destruction to Israel and ruin for many leaders and nations in this room".

The President's speech was interrupted with applause when he criticised the Iran nuclear deal, which the US signed under former president Barack Obama.

"We cannot let a murderous regime continue these destabilising activities while building dangerous missiles and we cannot abide by an agreement if it provides cover for the eventual construction of a nuclear program," he said.

"The Iran deal was one of the worst and most one-sided transactions the United States has ever entered into.

"Frankly, that deal is an embarrassment to the United States and I don't think you've heard the last of it - believe me."

MAJOR PARTS OF WORLD ARE 'GOING TO HELL'

Trump said "major portions" of the world were "going to hell" as part of his push for the UN to focus less on bureaucracy and more on results.

He outlined his views on UN reform in a speech on Monday, where he said the organisation had "not reached its full potential because of bureaucracy and mismanagement".

"While the United Nations on a regular budget has increased by 140 per cent, and its staff has more than doubled since 2000, we are not seeing the results in line with this investment," he said.

He elaborated on this comments on Tuesday: "Major portions of the world are in conflict and some in fact are going to hell but the powerful people in this room, under the guidance and auspices of the United Nations, can solve many of these vicious and complex problems."

Trump also complained that the US had funded a greater share of the UN than was fair and called on other nations to shoulder more of the burden.