An escalator used by Donald Trump abruptly stopped because of a safety mechanism that may have been triggered by his videographer, the United Nations has said.

The videographer had been travelling backwards up the escalator to capture the US president's arrival with First Lady Melania Trump and "may have inadvertently triggered the safety function" upon reaching the top, a UN spokesperson said.

Trump jokingly referred to the incident during his Tuesday speech at the UN building, saying: "If the First Lady wasn't in great shape, she would've fallen."

The White House had raised concerns that someone deliberately stopped the escalator as the couple were stepping on.

"If someone at the U.N. intentionally stopped the escalator as the President and First Lady were stepping on, they need to be fired and investigated immediately," White House press secretary Karoline Leavitt posted on X after the incident.

Stephane Dujarric, spokesperson for UN Secretary General António Guterres, said the videographer reached the top of the escalator as the president and first lady mounted the steps at the bottom.

"At that moment (09:50am), the escalator came to a stop," Dujarric said.

A readout of the machine's central processing unit "indicated that the escalator had stopped after a built-in safety mechanism on the comb step was triggered at the top of the escalator", he added.

The White House has not yet commented on the UN's findings.

After the escalator snafu, Trump ran into more technical difficulties as he began his speech to the UN General Assembly.

He opened by saying the teleprompter was not working - although it was restored towards the end of his address.

"I can only say that whoever's operating this teleprompter is in big trouble," he said.

A UN official later told the BBC the White House was operating the teleprompter at the time, bringing their own laptops and plugging them into the UN's system.

The official said this was because they would know the speed at which to run the text for the president.