There are reports of deaths and injuries after a blast near a car in a densely populated neighborhood of south Beirut, the stronghold of Hezbollah.
Hezbollah's Al-Manar television showed ambulances racing to the scene and burning wreckage.
Reuters news agency reported at least three deaths and about 20 injuries. The French news agency said five people died and at least 20 were wounded.
Television footage showed a charred automobile covered with leaves and rubble falling from balconies of nearby buildings.
The explosion comes less than a week after former Lebanese finance minister Mohamad Chatah, a harsh critic of Syrian President Bashar al-Assad, was killed in a massive car bombing in central Beirut.
Five other people were killed and about 70 wounded in that blast, which followed a series of sectarian bombings over the past year aimed at Shi'ite and Sunni Muslims in Lebanon.
In November, a double suicide bombing hit Iran's embassy, near the site of Thursday's explosion.