At least 53 people were wounded when a car bomb hit a shopping centre in Beirut's southern suburbs.
The blast happened in a stronghold of the Lebanese Shia Hezbollah militant group that has been fighting in Syria's civil war.
Tension in Lebanon has been high following the intervention of Hezbollah in support of Syrian President Bashar al-Assad.
Clouds of black smoke were seen rising over apartment blocks in the southern suburbs, which are home to many Hezbollah political offices.
Shopping areas would likely have been full ahead of the beginning of the Islamic holy month of Ramadan.
The attack is the second strike to hit Shia southern Beirut this year.
Two rockets hit the area in May and Lebanese security forces have also disarmed several rockets near Beirut in recent months.
It was unclear who was behind today's blast or May's attack.