Israeli fighter jets launched a series of massive airstrikes on a crowded area in the Lebanese capital Beirut on Friday, causing widespread destruction with fears of a large death toll.

At least 10 explosions rocked Beirut’s southern suburbs, a densely-populated area known as Dahiyeh, with large clouds of black smoke rising over the city. 

At least six residential buildings were flattened in the raids with extensive damage reported in nearby structures, according to Al Jazeera.

At least one large crater was seen at the site of the attack and filmed by local media, as dozens of rescue workers and paramedics rushed to the scene. 

Lebanon’s caretaker Prime Minister Najib Mikati said Israel’s attacks on Beirut’s southern suburb show it “does not care” about efforts to bring about a ceasefire.

Mikati’s press office sent a statement while he was in New York for the UN General Assembly.

Video of the strikes suggested they were carried out with ground-penetrating munitions known as bunker busters. In some footage, a vertical jet of flame was visible as a bomb appeared to explode beneath the ground.

Israeli media reported that Hezbollah Secretary-General Sayyed Hassan Nasrallah was the target and that the military was checking whether he had been hit. Sources close to Hezbollah told Reuters he was alive.

Friday’s strike in Beirut marked a major escalation by Israel, which has been gradually expanding deadly attacks on Lebanon in recent days. 

Prime Minister Benjamin Netanyahu’s office has circulated a photograph of what it says is the prime minister using a landline telephone to approve the strike, the New York Times reported. The newspaper said Netanyahu was returning from New York to Israel.

Jeanine Hennis-Plasschaert, the top UN official in Lebanon, said she was “deeply alarmed and profoundly worried about the potential civilian impact” of Israel’s “massive strikes”. 

More than 700 people, including dozens of children have been killed since Israel launched a massive bombing campaign in Lebanon on Monday.