Dozens of people have been killed by Israeli strikes in Lebanon, including 20 who died after a strike flattened a multi-story residential building in central Beirut overnight, according to Lebanese officials.

An Israeli airstrike killed at least 20 people in central Beirut on Saturday, Lebanon's health ministry said, one of the deadliest strikes on the heart of the capital since Israel began its assault against the Iran-backed Hezbollah group in September.

At least 20 people were killed in a powerful Israeli strike that flattened a multi-storey building in densely populated central Beirut, Lebanese officials said on Saturday, as more deaths were reported from Israeli attacks in eastern Lebanon.