New York attack: Trump orders 'extreme vetting' of foreign travellers

At least eight people were killed and 11 others injured in Lower Manhattan after a gunman in a truck ploughed through a busy bike path, an incident the US termed as an "act of terrorism".

The suspect, 29-year-old Sayfullo Saipov said to be from Uzbekistan, was shot in the stomach before being arrested.

"I have just ordered Homeland Security to step up our already extreme vetting programme. Being politically correct is fine, but not for this!" Trump tweeted.

Trump also changed the banner on his Twitter account to the New York skyline.

His administration announced last week that it would resume accepting refugees after a 120-day ban, though arrivals from 11 "high-risk" countries, most of them home to Muslim majorities, will still be blocked.

"Our thoughts and prayers are with the victims of today's terrorist attack in New York City and their families," Trump had said in a statement after the attack. Earlier, the US president took to Twitter to decry the attack, saying "we must not allow ISIS to return".

"In NYC, looks like another attack by a very sick and deranged person. Law enforcement is following this closely. NOT IN THE U.S.A.!" Trump tweeted.

"We must not allow ISIS to return, or enter, our country after defeating them in the Middle East and elsewhere. Enough!" he said in another tweet.

New York City Mayor Bill de Blasio said authorities are treating the incident as a terrorist attack. New York Governor Andrew Cuomo said there's no evidence to suggest there's a wider threat or plot, warning that people will still see more security forces out of caution.