BEIRUT, Lebanon (AP) — A massive explosion rocked Beirut on Tuesday, flattening much of the city’s port, damaging buildings across the capital and sending a giant mushroom cloud into the sky. More than 70 people were killed and 3,000 injured, with bodies buried in the rubble, officials said.

The blast struck with the force of a 3.5 magnitude earthquake, according to Germany’s geosciences centre GFZ, and it was heard and felt as far away as Cyprus more than 200 kilometres (180 miles) across the Mediterranean.

The sudden devastation overwhelmed a country already struggling with both the coronavirus pandemic and an economic crisis. For hours afterward, ambulances rushing in from around Lebanon carried away the wounded. Hospitals quickly filled beyond capacity, pleading for blood supplies, and generators to keep their lights on.

For blocks around the port, where the explosion took place, bloodied residents staggered through streets lined with overturned cars and littered with rubble from shattered buildings. Windows and doors were blown out kilometres (miles) away. Army helicopters helped battle fires raging at Beirut’s port.

The cause of the blast was not immediately known, but initial reports suggested a fire had detonated a warehouse at the port.

Abbas Ibrahim, chief of Lebanese General Security, said it might have been caused by highly explosive material that was confiscated from a ship some time ago and stored at the port. Local television channel LBC said the material was sodium nitrate. Witnesses reported seeing a strange orange-coloured cloud like that which appears when toxic nitrogen dioxide gas is released after an explosion involving nitrates.

The explosion came amid ongoing tensions between Israel and the Hezbollah military group on Lebanon’s southern border. Many residents reported hearing planes overhead just before the blast, fuelling rumours of an attack, though Israeli military overflights are common. An Israeli government official said Israel “had nothing to do” with the blast. He spoke on condition of anonymity because he was not authorized to discuss the matter with the news media. Israeli officials usually do not comment on “foreign reports”.

US Secretary of State Mike Pompeo extended his “deepest condolences” to the people of Beirut and said the United States is closely monitoring the situation. “Our team in Beirut has reported to me the extensive damage to a city and a people that I hold dear, an additional challenge in a time of already deep crisis,” Pompeo said in a written statement.

The blast was stunning even for a city that has seen civil war, suicide bombings and bombardment by Israel.

“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 meters (yards) from the port and was knocked off his feet by the force of the explosion.