Al Jazeera's James Bays, reporting from Beirut late on Friday, said gunfire also erupted outside the city's best known hotel, the InterContinental Phoenicia.
"This is a show of force by opposition fighters. They have taken positions next to a statue of Rafiq al-Hariri [the assassinated former Lebanese prime minister], and can be considered a statement to pro-government fighters that they are in control."
The street battles, which first erupted on Wednesday, have now left at least 13 people dead and 22 others wounded.
The clashes continued on Beirut on Friday as Hezbollah took control of large areas from groups loyal to the government after gun battles.
The building of Future TV network, owned by Saad Hariri, a prominent pro-government politician, was set alight by opposition fighters.
Lebanese troops began taking up positions in some neighbourhoods in west Beirut abandoned by the pro-government groups.
The army has largely avoided getting involved in the street battles amid fears of being dragged into the conflict.'Call for dialogue'
According to an opposition official, roadblocks will not be lifted around Beirut and the international airport until the government rescinds its measures against Hezbollah and sits down for a national dialogue.
Earlier in the day, a rocket-propelled grenade struck the fence of the heavily protected residence of Saad Hariri in the suburb of Koreitem, a Muslim area of western Beirut.
Hariri, leader of the Future bloc, the biggest party in Lebanon's governing coalition, was believed to be inside at the time but unhurt.
Earlier, armed men loyal to Hezbollah forced Future News, the news channel of the Future media group, off the air in Beirut.
"Gunmen surrounded the building, stormed into the garage and demanded that the army shut down the station," a senior TV official said.
Security sources said Hezbollah and fighters from the allied Amal movement - both Shia groups - had overrun offices of Hariri's Future conglomerate across the predominantly Muslim western half of the Lebanese capital.
The headquarters of the Future media group's Al-Mustaqbal daily was also surrounded by fighters firing rocket-propelled grenades, setting fire to one floor, its managing editor said.
Nadim Munla, the general manager of Future TV, told Al Jazeera that masked armed men entered the control rooms and cut off the cables.
"We have been effectively prevented from broadcasting and doing our jobs as media professionals," he said.
"Hezbollah ... have proven that the gun is stronger than the value of the opinion. We have only one thing left - free speech, and their guns will not silence us."
| Opposition fighters took rapid control of|
many suburbs of Lebanon's capital [AFP]
Lebanese troops evacuated the staff of the TV station's terrestrial and satellite studios in the Kantari area of western Beirut.
Against this backdrop of escalating tensions, Lebanese politicians appeared to be divided as ever, judging by their statements.
Michel Aoun, a Christian leader allied with the Hezbollah-led opposition, said that normalcy should be restored on the streets.
"The derailed carriage is now back on track. We hope from this point that things will fall back into the normal course [of events]," he said on Friday.
Aoun said he had sent a letter to Ban Ki-moon, the UN secretary-general, and various member states of the UN Security Council, but "did not find a clear response to avert the crisis".
For his part, Amin Gemayel, leader of the pro-government Kataeb Party, the mainly Maronite Christian party, urged Christians to stay away from the fighting.
He accused Hezbollah of staging a coup.
Separately, Walid Jumblatt, head of the pro-government Progressive Socialist Party and and leader of Lebanon's Druze community, said in an exclusive interview with Al Jazeera's Rula Amin, that he did not regret his backing for the removal of the head of security of Beirut airport, whom the government accused of being too close to Hezbollah.
"He said that the government should have undertaken these moves earlier, but predicts that the fighting will end soon," Amin said, referring to Jumblatt.
"I did not anticipate such a strong response from Hezbollah, but ... yes ... the group is much stronger than other armed militias," Jumblatt said.
He also said: "If you want to know what the next move for Hezbollah will be, ask [Mahmoud] Ahmadinejad [the Iranian president]. This situation goes beyond Lebanese borders."
On the ground, in several neighbourhoods of Beirut, automatic rifle fire could be heard in the worst domestic fighting since the 1975-90 civil war.
Hezbollah took control of all roads leading to Beirut's international airport, Lebanon's only air link to the outside world.
|Lebanese troops took control of several west|
Beirut suburbs from opposition fighters [AFP]
According to Elie Zakhour, a port official, Beirut's sea port was also shut down "until further notice" because of the situation, Lebanon's state-run National News Agency reported.
Tension between the government and Hezbollah escalated when the cabinet said the group's private phone network was illegal and an attack on the country's sovereignty.
Hezbollah said it was infuriated by government allegations it was spying on Beirut airport and by the cabinet's decision to fire the head of airport security.
The fighting has prompted urgent appeals for calm from the international community.
Saudi Arabia and Egypt called for an urgent meeting of Arab foreign ministers to try to halt the violence.
"An emergency meeting of Arab foreign ministers in Cairo to discuss the crisis will be held in two days," Hossam Zaki, the Egyptian foreign ministery spokesman, said.
The UN Security Council also called for "calm and restraint", urging all sides to return to peaceful dialogue.
Syria, an ally of Lebanon's opposition parties, said the dispute in Lebanon was an "internal affair" and expressed hope the feuding parties would find a solution through dialogue.
Al Jazeera's Mike Hanna, reporting from Jerusalem, said that Shimon Peres, the Israeli president, has called the clashes in Lebanon a "tragedy".
"The Israeli government does not view the current situation as a threat, but sees it as an internal matter," Hanna said.
"Israel, however, has always held the position that Hezbollah's intent is to split Lebanon."