As firefighters worked to douse a blaze sparked by the blast Red Cross ambulances evacuated the injured and dead, the Voice of America reported.
Lebanese officials say they believe top police investigator Wissam Eid, who died in the explosion, was the target of the bombers.
Eid had just finished meeting with members of the United Nations tribunal investigating the death of former Lebanese Prime Minister Rafiq al Hariri when the car bomb went off.
Ashraf Rifi, the head of Lebanon's national police force, said he thinks the assassination of Eid was intended as a "message to Lebanon's police and investigating community."
More than 30 major explosions have hit Lebanon since the 2005 assassination of Hariri, killing at least 10 top politicians, civil servants, law enforcement officers and journalists.
Most of the victims were in some way opponents of Syria.