Security sources said 20 people were killed in the southern Beirut district hit by an explosion on Thursday.
The powerful blast engulfed several cars in flames and also trapped people in a nearby building.
He said at least five nearby buildings were damaged and many cars in the area were destroyed. The blast sent a column ofblack smoke over the densely populated area in the south of the Lebanese capital.
The explosion came a month after a huge car bomb wounded 53people in the same district, a stronghold of Hezbollah which has been fighting alongside President Bashar al-Assad's forces in Syria's civil war.
Several minutes after Thursday's blast, live television footage showed fires still burning in the street where the explosion took place. The facades of neighbouring residential buildings were also badly damaged.
Al Mayadeen television said some people were still trapped inside buildings at the scene, close to the Sayyed al-Shuhadaa (Martyrs) complex, where Hezbollah leader Sayyed Hassan Nasrallah often addresses his followers.
Sectarian tensions have been high in Lebanon following the intervention of Shi'ite Muslim Hezbollah in support of Assad against a two-year revolt led by Syria's Sunni Muslim majority. Hezbollah also fought a month-long war with Israel in 2006.