An Associated Press photographer who went to the scene of the strikes said the first one, in the area of Ras al-Nabaa, appeared to have hit the lower half of an eight-story apartment building, and that explosions were ongoing inside the building.
A large number of ambulances arrived at the scene.
The second strike, in the area of Burj Abi Haidar, collapsed an entire building, which was engulfed in flames.
There was no immediate statement from the Israeli military.
In 24 hours, Lebanon's crisis response unit said Israeli shellfire and air strikes killed 28 people. (AP PHOTO)
In recent weeks Israel has launched frequent strikes on Beirut's southern suburbs, but strikes in central Beirut are rare.
The reports came as the Israeli military continued to pound Hezbollah targets across Lebanon.
Earlier in the day, an Israeli strike on a school sheltering displaced people in the Gaza Strip killed at least 27 people, Palestinian medical officials said.
The Israeli military said it targeted militants, but people sheltering there said the strike hit a meeting of aid workers.
Israel has continued to strike at what it says are militant targets across the Palestinian enclave even as attention has shifted to its war against Hezbollah in Lebanon and rising tensions with Iran.
The military launched a large-scale air and ground operation against Hamas in northern Gaza earlier this week.
In a separate development, the UN peacekeeping force in southern Lebanon said an Israeli tank fired on its headquarters in the town of Naqoura, hitting an observation tower and wounding two peacekeepers.
The attack drew widespread condemnation and prompted the Italian Defence Ministry to summon Israel's ambassador in protest.
The Israeli military acknowledged opening fire at a UN base in southern Lebanon on Thursday and said it had ordered the peacekeepers to "remain in protected spaces."
Over the last 24 hours, Lebanon's crisis response unit said Israeli shellfire and air strikes killed 28 people and wounded 113, bringing the total to 2,169 killed and 10,212 people wounded in Lebanon since the war erupted last October.
At least four people were killed on Thursday in the eastern Bekaa Valley, Lebanese health authorities said.
Hezbollah attacks have killed 28 civilians in northern Israel since the war began, as well as 39 Israeli soldiers, including both in northern Israel since last October and in southern Lebanon since Israel's invasion.
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