At least 53 wounded after car bomb rocks Beirut
None of those hurt were seriously wounded, Health Minister Hassan Khalil told Reuters, and there were no fatalities.
There was no immediate indication of who was behind the blast, the worst such attack in years, which came as forces loyal to Assad are making gains on the battlefield and as Sunnis and Shi'ites clash in Lebanon.
But residents in the Shi'ite district blamed Sunni militant supporters of the insurgency against Assad, while politicians also suspected a sectarian motive.
"This is the work of agents trying to create strife in Lebanon," Hezbollah parliamentary deputy Ali Meqdad said at the site of the explosion.
Interior Minister Marwan Charbel said the attack was "a criminal act aimed at destabilising the country and creating Sunni-Shi'ite sectarian strife". President Michel Suleiman said it reopened the "black pages" of Lebanon's civil war.
Syria's conflagration has spread to Lebanon, where there have been outbreaks of fighting reflecting the renewed sectarian tension now spreading through the Middle East.
Lebanon's Sunni Muslims mostly support the rebels in Syria, while Shi'ites have largely supported Assad, who is part of the minority Alawite sect, an offshoot of Shi'ite Islam.
Sunni militant groups have threatened to attack Hezbollah following its military intervention in Syria. Hezbollah did not immediately respond to Tuesday's blast but it has made clear it intends to keep fighting alongside Assad's forces in Syria.
A Reuters reporter saw a large fire raging at the site of the blast near a shopping mall in Bir al-Abed, an area that is also home to Hezbollah officials and their offices. It was unclear if any of the group's leaders had been in the area.
A pillar of dense black smoke billowed above surrounding high-rise apartment blocks. Ambulances and fire engines sped through the streets to rescue casualties.
Dozens of cars were ablaze in the parking lot where the car rigged with explosives was left. Reuters and other media outlets were prevented from reaching the area, where Hezbollah gunmen allowed only the group's Al Manar TV to operate.
Images from the scene showed a crater covered by a blue tarpaulin and surrounded by wrecked cars. Hezbollah men with red caps and yellow arm-bands set up a security cordon around the blast scene along with Lebanese soldiers.
Hezbollah gunmen were seen arresting two men near the scene.
Angry young men carrying pictures of Hezbollah leader Sayyed Hassan Nasrallah began shouting "God and Nasrallah".
Soldiers fired in the air to dispel crowds trying to attack interior minister Charbel, who has in the past declined to crack down on hardline Sunni groups in Lebanon.
Zeinab, a 45-year-old woman whose apartment opposite the blast site had its windows blown out, broke down in tears.
"I went to fetch breakfast for my son and then heard the explosion. I want to know he is OK. I want to talk to him."
Shopping areas would likely have been full on Tuesday, the day before the Islamic holy month of Ramadan begins. Most of the casualties were apparently women and children out shopping.
The attack is the second strike in Shi'ite southern Beirut this year. Two rockets struck the area in May.
No group claimed responsibility for Tuesday's blast but shocked and angry residents were quick to blame Sunni militants.
Hajje Alia, a 35-year-old woman clad in a black robe, said: "We have been expecting explosions in this holy month of Ramadan from the Takfiris (Sunni militants) who are trying to stop us from carrying out our holy war duties alongside our Syrian brothers, but nothing will stop us, not even 1,000 explosions."
The last car bomb to hit Beirut targeted a senior intelligence official in October. Wissam al-Hassan was part of the country's leading Sunni opposition party, which has supported the uprising in Syria.
Hezbollah leader Nasrallah has promised that his group will continue fighting for Assad after it spearheaded the recapture of the strategic town of Qusair last month.
Abu Ali, who lives near the blast scene, blamed what he called Sunni terrorists for the attack.
"They want to terrorise us. The scumbags. These terrorists want us to abandon (the leader of Hezbollah) but we swear we will love him more, for all our lives. All we own, and our children we pledge to him."