Israel has intensified its attacks on Lebanon as jets launched fresh strikes on Beirut airport, the road to the Syrian capital and a power plant.
The overnight strikes followed warning leaflets from Israel
The Israelis concentrated on the southern suburbs of the city, known as a stronghold of Hezbollah militants.
The offensive, which has killed more than 50 Lebanese civilians since Wednesday, follows the capture of two Israeli soldiers by Hezbollah.
The escalation has sparked international calls for restraint.
The UN Security Council is due to hold an emergency meeting later on Friday. Lebanon has urged it to adopt a resolution calling for a ceasefire.
Crushed in car
Israel says it struck 18 Hezbollah targets in the latest sea and air attacks, killing three civilians and wounding at least 50.
ISRAEL IN LEBANON
March 1978: Israel invades to stop Palestinian attacks
1982: Full-scale invasion; Israel occupies Beirut; pro-Israel militias massacre Palestinian refugees
May 1983: Israel pulls back, but keeps "security zone"
February 1992: Israeli air strike kills Hezbollah leader
1996: Israel launches "Grapes of Wrath" raids on Hezbollah; 100 civilians die under Israeli shelling of UN base at Qana
May 2000: Israel withdraws troops from Lebanon
January 2004: Prisoners-bodies swap agreed between Hezbollah and Israel
Ground forces responded with anti-aircraft fire, as planes flew over the city.
Israel had warned that the south of the city could be targeted - telling residents by leaflet to stay away from Hezbollah locations.
Residents said two of the victims were crushed to death in their car following the collapse of a bridge on the road to the airport.
The Israelis also struck a fuel storage tank at the Jiyyeh power plant.
Black smoke rose from southern Beirut, as firefighters fought blazes. Some areas are now without power.
Workers with bulldozers have started repairs to roads damaged by the attacks, which correspondents say have not paralysed the area.
Residents hoarded food and queued for petrol, amid fears of prolonged violence.
Lebanese police also reported a strike on a pro-Syrian Palestinian group, less than 2km (1.2 miles) from the Syrian border.
For their part, Hezbollah continued to fire rockets into Israel. At least two Israelis have been killed and dozens injured in such attacks over the past two days.
On Thursday, one rocket hit Haifa, Israel's third-largest city. Hezbollah denied firing it, but Israel described the incident as a "major escalation" of the crisis.
'Playing with fire'
UN Secretary General Kofi Annan has said he is "profoundly worried" by the violence and will send a high-level team to the Middle East.
But Israel said the international community should make it clear to Iran and Syria - which Israel says form an "axis of terror" with Hezbollah and Palestinian militants Hamas - that they were "playing with fire".
Iranian President Mahmoud Ahmadinejad told Syrian President Bashar al-Assad in a telephone call that there would be a "fierce response" to any Israeli attack on Syria.
Syria has said Washington should use its power to end Israel's attack on Lebanon.
The US says Israel should exercise restraint but is also demanding that Syria put pressure on Hezbollah to stop attacks on Israel.
The Israeli offensive follows a day of heavy fighting on Wednesday in which the Israelis suffered their worst losses on the border for several years.
Eight soldiers were killed and two were injured, in addition to the two captured in a Hezbollah ambush.
Hezbollah has said the captured soldiers will not be returned without a release deal for Palestinian, Lebanese and other Arab prisoners held in Israeli jails.
Israel is also continuing a separate offensive in the Gaza Strip. An Israeli soldier was captured there last month.
ISRAEL BLOCKADES LEBANON
Two rockets hit Israeli city of Haifa on Thursday evening
Israel targets Lebanon by land, air and sea: enforcing naval blockade, bombing Beirut airport and shelling Lebanese towns
Jets also hit a Beirut power plant, the road to the airport and the highway from Beirut to the Syrian capital
Jets bomb Lebanese army air base at Rayak and Baalbek TV transmitter in Bekaa Valley
Shelling from both sides is heaviest over Lebanon's southern border
Hezbollah targets Kiryat Shmona, Nahariya and Safed in Israel