Watch: World leaders laugh at Trump during UN speech

Donald Trump's speech to the United Nations' general assembly has provoked a bemused reaction after he boasted about his accomplishments as leader.

"In less than two years, my administration has accomplished more than almost any administration in the history of our country," the US President said.

The assembly rumbled with laughter at the comments, prompting Mr Trump to stop the speech for a moment to respond.

"I didn't expect that reaction but that's okay," he said.

However one person who wasn't laughing was Prime Minister Jacinda Ardern.

"I didn't laugh. I was listening to the words being spoken... The President made a statement around his view around his success relative to past presidents," she told media after Mr Trump's speech.

"For me, I was respecting the fact he had the floor and what he had to say."

But she said she "certainly wouldn't" follow Mr Trump's example by boasting about her accomplishments.

"New Zealanders, as self-deprecating as we are, never tend to talk about ourselves in particularly grandeur statements. I certainly wouldn't," she told media.

"I think it's up to our voters to determine our place in history."

What did Donald Trump's speech say?

Mr Trump devoted a large portion of the rest of his speech to Iran as relations between the two countries became strained since the US pulled out of the Iran agreement in May.

The 2015 agreement saw sanctions on Iran lifted in return for stopping its nuclear programme, but Mr Trump has labelled it a "horrible one-sided deal".

During the speech he called Iran's administration a "corrupt dictatorship" that takes advantage of its citizens to pay for aggression overseas.

"Iran's leaders sow chaos, death and destruction," Mr Trump told the annual gathering on Tuesday.

"They do not respect their neighbours or borders, or the sovereign rights of nations."

Iranian President Hassan Rouhani is also at the United Nations, but Mr Trump will not be meeting with him.

"Despite requests, I have no plans to meet Iranian President Hassan Rouhani. Maybe someday in the future. I am sure he is an absolutely lovely man," Mr Trump wrote in a post on Twitter on Tuesday.

Mr Rouhani said on Monday Tehran would not be interested in speaking with the US President until he returned to the 2015 deal.