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.

Israeli airstrikes Saturday in central Beirut killed at least 20 people, officials said, as the once-rare attacks on the heart of Lebanon's capital continued without warning while diplomats scrambled to broker a cease-fire.

At Kamal Adwan Hospital, one of three medical facilities on the northern edge of Gaza that is barely operational, director Hussam Abu Safiya said the ongoing Israeli bombardment appeared aimed at forcing hospital staff to evacuate - something they have refused since the incursion began.