Opposition supporters have been holding street celebrations after President George Weah conceded election defeat to Joseph Boakai. / Photo: Reuters

Two people died and at least 20 were injured when a car ploughed into a crowd of supporters of Liberian president-elect Joseph Boakai, police and hospital staff said on Tuesday.

Police did not give a reason for the incident, which occurred on Monday evening, but a spokesman for Boakai's Unity Party said they believed it was a deliberate act.

The driver had fled the scene, police said.

"Two people are dead and one is in critical condition," said Sia Wata Camanor, a senior member of staff at the John F. Kennedy (JFK) hospital in the capital, Monrovia.

Twenty others had been injured, she told AFP news agency.

Police were searching hospitals for other victims.

Boakai's party initially said at least 10 people were killed when a car drove into a group of supporters celebrating outside their headquarters around 9pm local time (2100 GMT).

Bloody videos

"It just picked up with speed and ran into the supporters, and as we speak about 10 people are dead," party spokesman Mohammed Ali told AFP.

Videos posted on social media showed bloodied people lying on the ground, some receiving medical assistance.

Boakai was officially declared the winner of last week's election on Monday with 50.64 percent of the vote, against 49.36 percent of the vote for incumbent George Weah.

The outgoing president and former football star won praise abroad for conceding and promoting a non-viol ent transition in a region marred by coups.