Trump spent nearly an hour in the bunker, which was designed for use in emergencies like terrorist attacks, according to a Republican close to the White House who was not authorised to publicly discuss private matters and spoke on condition of anonymity.

The account was confirmed by an administration official also on condition of anonymity.

The abrupt decision by the agents underscored the rattled mood inside the White House, where the chants from protesters in Lafayette Park could be heard all weekend and Secret Service agents and law enforcement officers struggled to contain the crowds.

Friday's protests were triggered by the death of George Floyd, a black man who died after he was pinned at the neck by a white Minneapolis police officer.

The demonstrations in Washington turned violent and appeared to catch officers by surprise. They sparked one of the highest alerts on the White House complex since the September 11 attacks in 2001 .

"The White House does not comment on security protocols and decisions," said White House spokesman Judd Deere.

The Secret Service said it does not discuss the means and methods of its protective operations. The president's move to the bunker was first reported by The New York Times.

The president and his family have been shaken by the size and venom of the crowds, according to the Republican.

It was not immediately clear if first lady Melania Trump and the couple's 14-year-old son, Barron, joined the president in the bunker.

Secret Service protocol would have called for all those under the agency's protection to be in the underground shelter.

Australian Associated Press