President Donald Trump on Monday signed a law ensuring lifelong medical help for emergency crews sickened by toxic debris on 9/11, while claiming considerable experience of his own at New York's Ground Zero.

Trump, a native New Yorker long synonymous with the city's real estate industry, claimed that he had taken part in the hellish post-9/11 response at Manhattan's Ground Zero.

"I was down there also. But I'm not considering myself a first responder, but I was down there. I spent a lot of time down there with you," he told the first responders at the White House.

It's not clear how much time, if any, Trump spent in Ground Zero, as the area was quickly sealed off by law enforcement.

Trump has previously claimed, without evidence, that he sent more than 200 workers to join the Ground Zero clean-up.