BEIRUT – A massive explosion rocked Beirut on Tuesday, flattening much of the port, damaging buildings across the capital and sending a giant mushroom cloud into the sky. More than 70 people were killed and thousands were injured, with bodies buried in the rubble.

Hours later, ambulances still carried away the wounded as army helicopters helped battle raging fires.

The sudden devastation overwhelmed a country already struggling with both the coronavirus pandemic and an economic crisis: Beirut hospitals quickly filled beyond capacity, pleading for blood supplies and generators to keep their lights on.

The cause of the blast, which sparked fires, overturned cars and blew out windows and doors, was not immediately known.

Abbas Ibrahim, chief of Lebanese General Security, said it might have been caused by highly explosive material confiscated from a ship some time ago and stored at the port.

TV station LBC said the material was sodium nitrate. Witnesses reported seeing a strange orange-colored cloud over the site after the explosion. Orange clouds of toxic nitrogen dioxide gas often accompany an explosion involving nitrates.

An Israeli government official, speaking on condition of anonymity, said Israel "had nothing to do" with the blast.

The explosion was stunning even for a city that has seen civil war, suicide bombings and bombardment by Israel. It could be heard and felt as far away as Cyprus, more than 180 miles across the Mediterranean.

"It was a real horror show. I haven't seen anything like that since the days of the [civil] war," said Marwan Ramadan, who was about 500 yards from the port and was knocked off his feet.

Health Minister Hassan Hamad said the preliminary toll was more than 70 dead and more than 3,000 wounded. Emergency teams streamed in from across Lebanon to help, and the injured had to be taken to hospitals outside the capital. Hamad added that hospitals were barely coping and offers of aid were pouring in from Arab states and friends of Lebanon.

A civil defense official said there were still bodies inside the port, many under debris.

Beirut governor Marwan Abboud broke into tears as he toured the site, saying, "Beirut is a devastated city."