A large explosion rocked a Hezbollah stronghold in the Lebanese capital early Tuesday, sending black smoke billowing into the sky, security officials said.
At least 18 people were wounded, security sources said.
The sources were unable to confirm initial reports from medics at the scene that an unspecified number were killed in the massive blast.
Hezbollah sealed off the site of the explosion, a shopping mall run by the group in the the Bir al-Abed district.
The officials said it was not clear whether the blast in the suburb of Beir el-Abed in south Beirut was caused by a car bomb. The officials, who spoke on condition of anonymity in line with regulations, said it was near a gas station.
Hezbollah's Al-Manar TV said the blast was a car bomb inside a parking lot near an Islamic center. The station broadcast footage of a thick plume of smoke rising into the sky at the site of the blast as people rushed to take casualties to the hospital.
"I haven't heard an explosion like this one since the 1980s(when a car bomb targeted Hezbollah's late spiritual leader Sayyed Mohammed Hussein Fadlallah)," a woman in southern Beirut said.
Some Syrian rebel groups have threatened to strike in Lebanon after Hezbollah joined Syrian President Bashar Assad's troops in their battle against opposition fighters.
In May, two rockets slammed into a Hezbollah stronghold in south Beirut, wounding four people. The rockets struck hours after Hezbollah leader Sheikh Hassan Nasrallah vowed in a speech to help propel Assad to victory in Syria's civil war.
Hezbollah has openly joined the fight in Syria, and the group's fighters were instrumental in a recent regime victory when government forces regained control of the strategic town of Qusair near the Lebanese border.