A car bomb in the centre of Beirut is reported to have killed Lebanese former minister Mohamad Chatah and several other people.
Mr Chatah, a leading figure opposing the regime of Syrian President Bashar al-Assad, was on his way to attend a meeting when the bomb went off.
A witness at the scene said his car was "totally destroyed. It is a wreck."
Mr Chatah, a Sunni Muslim, was a formerex-minister of finance and Lebanon's envoy to Washington under Rafik al-Hariri, who was also killed in a car bombing.
The ABC reported the sound of the blast was heard across the city at around 9:40am local time, and a plume of black smoke was seen rising in the downtown business and hotel district.
Lebanon's state news agency reported that 50 people were wounded in the bombing.
Footage broadcast by Future TV showed people on fire and others lying on the ground, some bloodied. Ambulances could be seen taking victims from the area.
A restaurant and a coffee shop were destroyed in the blast, and several cars were on fire, the witness said, adding that there was glass everywhere and the smell of explosives filled the air.
Much of Beirut went into lockdown following the explosion, with police blocking off roads across the city.
Beirut has been hit by several deadly attacks over the past months, including twin suicide bombings in November that targeted the Iranian embassy and bombings in the bastion of the Shiite movement Hezbollah in the south of the capital over the summer.
Mr Chatah was also an outspoken critic of Hizbollah.