Israel used internationally banned white phosphorous bombs in a strike on an apartment building in the residential Bashoura district in the early hours of Thursday, Lebanon's state news agency NNA reported.
The strike started a fire in the heavily-populated Beirut district close to Lebanon's parliament and UN headquarters, according to comments from the prime minister's office and the Lebanese parliament.
It hit the office of a medical centre run by the Hezbollah-affiliated Health Society killing nine people and injuring 14 others.
The organisation said seven of its staff, including two medics, were killed in the attack.
Residents in Beirut reported a sulfur-like smell in the city following the airstrike. The attack came without any prior warning or evacuation order from Israeli forces. Residents living in nearby areas began to flee, driving away quickly in scooters and cars.
Videos circulating online showed the floor of an apartment building burning.
Human rights groups have in the past accused Israel of using white phosphorus incendiary shells on residential buildings in towns and villages in conflict-hit southern Lebanon.
Israeli strikes in central Beirut are rare. The attack is the first Israeli airstrike to hit the centre of Lebanon's capital since the war between the two countries in 2006.
Multiple strikes were also reported in Beirut's southern suburbs as Israeli forces issued new evacuation orders for five buildings in the Dahiyeh area.
The Lebanese health ministry said a further 46 people had been killed in Israeli attacks on the city in the last 24 hours.