A huge car bomb rocked central Beirut on Friday, killing six people including an influential member of a coalition opposed to the Syrian regime, and leaving cars ablaze and buildings wrecked.

State news agency NNA said that Mohammad Chatah, 62, died as he headed to a meeting in the city centre of the March 14 coalition at the mansion of ex-prime minister Saad Hariri. Dozens were injured in the blast.

Chatah, an influential economist and former minister of finance and Lebanon's envoy to Washington, had served as adviser to ex-premier Fuad Siniora and remained a close aide to his successor, Saad Hariri.

Footage broadcast by Future TV showed people with their clothes on fire, others lying on the ground, some bloodied and in shock, as well as the mangled remains of a burning car.

Ambulances as well as security reinforcements rushed to the stricken area, where people caught in the blast were seen walking about in a daze as crowds gathered.

The blast sent thick black smoke scudding across the capital's skyline and over the Grand Serail, a massive Ottoman-era complex that houses the offices of the Lebanese prime minister.

NNA news agency gave an initial toll of five people killed and more than 50 wounded in the blast, and said that more than 10 buildings in the area were badly damaged.

The prosecutor general Samir Hammud announced that the explosive had been between 50 and 60 kilogrammes.

There was no immediate claim of responsibility for the early morning bombing, the first in recent times to have struck the commercial and banking district of Beirut, which is also home to government offices and parliament.

But Sunni leader Hariri was quick to implicate the powerful Shiite movement Hezbollah in the attack, and linked the group to his father Rafiq Hariri's murder nearly nine years ago in another massive car bomb attack.

An hour before he was killed Chatah, tweeted a message slamming Hezbollah.

"Hezbollah is pressing hard to be granted similar powers in security & foreign policy matters that Syria exercised in Lebanon for 15 years," he said, in reference to Syria's nearly 30-year military and political hegemony in Lebanon that ended after Rafiq Hariri's 2005 murder.

French President Francois Hollande denounced the "cowardly attack", in the first reaction by a world leader.

The Serail sits atop a hill, towering over a vibrant city centre which was destroyed in 1975-1990 civil war.

Rafiq Hariri had overseen the rebuilding of downtown Beirut, which houses the parliament building, modern glass towers, shops, cafes and restaurants and is known for its night life and tourist attractions.

"We were opening our store when we heard the blast. It was really loud. We are used to blasts in Lebanon but not in this area. Now we are not safe anywhere," said shop attendant Mohammad, 23.

Ziad, a 37-year-old businessman whose office is located near the scene of the attack, told AFP: "Chatah was a really respectful person... I was so shocked he has been killed."

The attack was a grim reminder that the violence that tore Lebanon apart during the civil war is never far away, and comes as conflict raging across the border in Syria.

The 33-month civil war, which has reportedly killed more than 126,000 people, has deepened political and sectarian divisions in Lebanon, and sparked often deadly fighting between opponents and supporters of the Syrian regime.

'Those who have spread the regional fire'

Hariri said those responsible for Chatah's murder, are "those who are hiding from international justice and who have spread the regional fire to the (Lebanese) nation... and who killed Rafiq Hariri."

He was clearly referring to Hezbollah, whose fighters are helping Syrian regime troops battle rebels supported by Hariri's March 14 anti-Syria coalition.

Hezbollah has also refused to hand over suspects wanted by a UN-backed tribunal investigating the murder of Rafiq Hariri and 22 others in a massive Beirut seafront bombing.

Five Hezbollah members are to be tried in absentia by the Special Tribunal for Lebanon in The Netherlands, with the first hearing set for January 16.

The country has been hit by several deadly attacks linked to the Syria war, including a double suicide bombing in November that struck the Iranian embassy in Beirut and killed 25 people. Hezbollah strongholds in the south of the Lebanese capital were hit twice, in July and August.

Lebanon has been without a government for months over deep divisions between Hezbollah and the parties opposed to its involvement in Syria.

Many in Lebanon resent that Hezbollah -- which is blacklisted by the United States and the European Union -- refused to disarm at the end of the civil war on the grounds that it must fight Israel.