Gunfire and the thump of exploding rocket-propelled grenades echoed across mainly Muslim west Beirut, where the fighting was concentrated between Sunni militants loyal to the Western-backed government and Shiite opposition gunmen.

At least 11 people been killed and dozens more wounded in the street battles that erupted Thursday after Hezbollah chief Hassan Nasrallah said a government crackdown on his Iranian-backed Shiite Muslim group was a declaration of war.

The unrest has triggered urgent appeals for calm from the international community amid fears that a protracted political feud in multi-confessional Lebanon could plunge the country back to the dark days of the 1975-1990 civil war.

Many residents of west Beirut were fleeing to seek shelter elsewhere as tanks rolled through the streets and hundreds of riot police and troops patrolled the city, but did not get involved in the fighting.

Leaders of Lebanon's ruling coalition have been called to an emergency meeting while Arab nations are pushing for a special session of foreign ministers to tackle the crisis. Some states have begun evacuating residents.

"West Beirut plunges into urban warfare," thundered the French newspaper L'Orient-Le Jour.

Lebanon's already debt-laden economy could also be hard hit, with the enforced shutdown of the country's only international airport and the Beirut port and several major highways blocked by burning tyres.

Witnesses and AFP correspondents said several Sunni neighbourhoods in west Beirut considered bastions of Lebanon's ruling bloc had been overrun by militants from Hezbollah and its ally Amal.

Fierce gunbattles also raged in the mixed Sunni-Shiite-Christian neighbourhood of Hamra where opposition militants also appeared to be gaining ground, AFP correspondents saw.

"Everyone is running away," said 35-year-old businessman Imad in a west Beirut neighbourhood as people rushed to stores that remained open to stock up, while others remained trapped in their homes by the fighting.

Armed militants were prowling about or hiding in buildings in the otherwise deserted streets of the capital, but by midday the fighting appeared to have eased.

"It was a hellish night. The armed militants were everywhere shooting all over the place," said Rima, another west Beirut resident.

Hezbollah, the most powerful armed movement in Lebanon, has also forced the shutdown of all media belonging to the family of parliamentary majority leader Saad Hariri, while a rocket hit the outer perimeter of his Beirut residence.

Hariri, whose father Rafiq Hariri was assassinated in 2005, had made a television appeal to try to calm the situation but this was rejected by Hezbollah.

Gunmen firing rocket-propelled grenades surrounded the headquarters of the Hariri's Future Television and his movement's Al-Mustaqbal newspaper early Friday, forcing all its media outlets to close.

"The army is in control of institutions placed under its authority, such as the media outlets of the Future Movement," the army said.

"It also controls the area around the government headquarters, the central bank, major roads and the area where Hariri and Jumblatt's residences are located in west Beirut," referring to prominent Druze leader Walid Jumblatt.

Air traffic was paralysed for the third straight day with no flights scheduled to land or take off from Beirut international airport, an airport official said, after Hezbollah supporters blocked access with mounds of earth and burning tyres.

Nasrallah delivered his defiant speech on Thursday after the government launched a probe into a private communications network run by Hezbollah, which is seen in the West as a terrorist outfit and which critics say has become a "state within a state."

"The decisions are tantamount to a declaration of war and the start of a war... on behalf of the United States and Israel," Nasrallah charged. "The hand that touches the weapons of the resistance will be cut off."

The United States delivered a blunt warning to Hezbollah to stop its "disruptive activities" while UN Security Council members said they were "deeply concerned" over the crisis, a view reflected by other Arab and European leaders.

The crisis will be the focus of talks between President George W. Bush and Lebanese Prime Minister Fuad Siniora in Egypt next week during the US leader's tour of the Middle East.

Regional powerhouse Saudi Arabia, which backs the Siniora government, called for an urgent meeting of Arab foreign ministers, while Yemen suggested army chief Michel Sleiman be mandated to chair a dialogue to resolve the crisis.

The long-running political standoff, which first erupted in November 2006 when six pro-Syrian ministers quit the cabinet, has left the country without a president since November, when pro-Syrian Emile Lahoud stepped down.

While the rival factions have agreed on Sleiman as a consensus candidate, they disagree on the make-up of the new cabinet and so far 18 sessions of parliament to choose a president have been cancelled.

"For the entire country, it is now a question of life or death," L'Orient-Le Jour said. "Nasrallah offered the government no other alternative than a humiliating retreat or war."

© 2008 Agence France-Presse