U.S. President Donald Trump on Tuesday reiterated his calls to governors to clamp down on "lowlife" protests across the country as leaders across the world continue to condemn the killing of an unarmed black by police last week.

George Floyd died on Monday last week after a white police officer knelt on his neck for several minutes as he and his colleagues arrested him.

An onlooker's cell phone recorded the incident showing the 46-year-old black man moaning, "Please, I can't breathe" and "Don't kill me" as the police officer pressed his knee onto Floyd's neck. However, the video didn't show how the confrontation started.

After several minutes of the police office pressing his knee on Floyd’s neck, the victim went silent and was later pronounced dead.

The video quickly went viral on social media, sparking widespread protest from Tuesday afternoon, some of which have deteriorated into chaos.

"NYC, CALL UP THE NATIONAL GUARD. The lowlifes and losers are ripping you apart. Act fast! Don’t make the same horrible and deadly mistake you made with the Nursing Homes," Trump Tweeted as protests rocked the U.S. for an eighth straight day.

He went on to accuse the New York City leadership of laxity, saying: "New York City put on an 11:00 P.M. CURFEW last night. No wonder they ripped the place apart. Should be 7:00 P.M. CALL UP THE NATIONAL GUARD."

More than 20,000 National Guard members have been called up in 29 states to deal with the unrest. New York is not among them.

Various leaders globally have condemned Floyd’s killing and have called for justice to his family.

In an address on Tuesday, former U.S. vice president Joe Biden said the Trump administration’s response to the protests showed a lack a leadership in the U.S.

"A country is crying out for leadership. Leadership that can unite us, leadership that brings us together, leadership that can recognize the pain and deep grief of communities that have had a knee on their neck for a long time," he said.