A witness said at least two people were killed by the blast, which sent a column of smoke into the sky over the Lebanese capital, according to Reuters.
The explosion hit the Haret Hreik district during rush hour and images broadcast on Hezbollah's Al-Manar TV showed firefighters putting out several cars that were ablaze.
The footage showed at least one building that had its facade blown off, and several neighbouring buildings were also damaged.
Beirut has been hit by a series of bombs in recent months, including one last week which killed a former minister and political adversary of the Shiite Hizbollah group.