The area contains strongholds of the Shia militant movement Hezbollah.

The explosion happened in a densely populated part of the capital. Heavy damage was reported to nearby buildings and cars.

The blast is being linked to the conflict in Syria, which has worsened sectarian tensions in Lebanon.

Plumes of smoke rose over the area where the blast occurred, between the Bir Abed and Rweiss districts of the city.

Lebanese officials said that the blast was the result of a car bomb.

The bomb appeared to have gone off between two apartment buildings, the BBC's Jim Muir reports from the scene.

The street was jammed with ambulances and fire trucks, our correspondent reports.

Few would doubt the blast was a result of Hezbollah's involvement in the conflict in Syria, he says.

Fighters from the militant group were instrumental in a strategic victory by Syrian government forces in Qusair, close to the border with Lebanon, in early June.

Events in Syria are putting Lebanon's fragile peace in jeopardy, correspondents say, threatening the equilibrium which has held since the end of the civil war over 20 years ago.

Last month, a bomb in a nearby area of southern Beirut injured more than 50 people and injured dozens.