Donald Trump has criticised other countries' migration and climate policies, during a scathing speech to the United Nations that also took aim at the body itself.

He told the UN's General Assembly in New York it was time to end the 'failed experiment of open borders' and claimed UN predictions over climate change were wrong, prompting gasps from the assembly floor.

In a wide-ranging speech stretching to almost an hour, Trump also repeated claims to have stopped 'seven wars' since returning to the White House and accused the UN of failing to help him do so.

He queried the UN's purpose and said it was 'not living up to its potential'.

Though the reaction from delegates was largely muted, some were visibly squirming in their seats as the US president addressed the UN for the first time since he began his second term.

Several could be seen shaking their heads as he denied climate change, calling it the 'greatest con job ever perpetrated on the world' and refuted the use of renewable energy.

'...asking successful industrialised nations to inflict pain on themselves and radically disrupt their entire societies must be rejected completely and totally,' he told his audience.

The overwhelming majority of scientists and experts agree that climate change is caused by humans and is real.

Trump also levelled criticism at UN assistance for asylum seekers, saying the organisation was 'funding an assault on western countries' by offering cash support.

He singled out Europe, saying it was in 'serious trouble' over migration.

'...we have to solve the problem in their countries,' he said.

Trump falsely claimed that London wanted to move to follow Sharia law - an Islamic legal system - and singled out the city's mayor Sir Sadiq Khan for criticism.

... he said a ceasefire was needed in Gaza but criticized the move from some countries to recognize a Palestinian state, saying it 'would be a reward' for Hamas.

... he said it was 'embarrassing' that some European nations were buying oil and gas from Russia even as they oppose its full-scale invasion of Ukraine.

After the address, Trump said he believed the speech had been 'very well received' in a post on his Truth Social platform.

... Trump is also set to meet officials from several Middle Eastern countries, including Qatar, Saudi Arabia, and Egypt...