An explosion was heard in one of Beirut's Muslim neighbourhoods late on Monday, residents and television stations reported.
One Lebanese television station said at least four people were injured in the explosion near the Verdun shopping area in the Sunni Muslim sector of Beirut.
Hezbollah's Al-Manar television said the explosion occurred in a car park near the Russian Cultural Centre in the posh district.
Television footage showed a car burning near a building as a fire engine doused the flames with water. An elderly man with a wound to his head was seen being carried away by pedestrians.
Several nearby cars had their windows blown out from the blast, and a high-floor apartment in a nearby building was in flames.
Pieces of wood and glass littered the streets and hung from balconies, as security and civilians crowded the scene.
On Sunday night, a bomb near another major shopping centre in the Christian sector killed a woman and wounded 12 others.
The violence came as Lebanese troops fought heavy battles with militants in northern Lebanon's Palestinian refugee camp of Nahr el-Bared, in which more than 50 people were killed in the last two days.
Beirut and surrounding suburbs have been hit by a series of explosions in the last two years, particularly targeting Christian areas in which the US-backed majority coalition has blamed on Syria.
Sunday's explosion occurred across the street from the major ABC shopping centre shortly before midnight in Ashrafieh, an upscale neighbourhood of the Christian sector of the Lebanese capital.
A 63-year-old woman was killed and 12 others injured.
The explosions also come as the UN Security Council is considering whether to impose an international tribunal in the assassination of former Premier Rafik Hariri after Lebanon's government and the Shiite Muslim Hezbollah-led opposition failed to agree on approving it.
A UN investigation into the 2005 assassination has been expanded to include the series of bombings some blame on Syria.
A UN investigation has linked senior Syrian security officials and allies in the Lebanese security services to Hariri's 2005 truck bombing murder while Syria controlled Lebanon.
Damascus has denied involvement in Hariri's death and the other explosions, but Syria was forced to withdraw its army from Lebanon two months after the assassination, ending a 29-year presence.