Shia gunmen led by Hezbollah have seized most of the western half of Beirut, driving out supporters of the Western-backed government.
Burning road blocks have been erected across the city during three days of violence, which was triggered by a government move on Monday to shut down Hezbollah's telecoms network.
At least 11 people are dead and scores injured, while cars have been torched and property smashed in some of the worst internal strife seen in the Lebanese capital since the 1975-90 civil war.
The gunmen forced the closure of governing coalition leader Saad Hariri's TV and radio stations and his newspaper. The Lebanese army later took over the buildings to guard them.
The gunmen detained Sunni government supporters and over-ran Sunni areas of west Beirut. Despite sectarian strains, the conflict is said to remain mostly political.
The Lebanese army command has warned its unity is at risk if the crisis in the capital drags on.
Analysts say the key to staving off a descent into civil war may lie in how long the army can stay neutral.
As residents of west Beirut fled on Friday, the Italian government was reported to be drawing up an evacuation plan for any of its nationals wanting to leave the city.
But with road blocks all but closing down Lebanon's international airport, many passengers trying to board flights out of the city had to make their way to the terminal building on foot.