BEIRUT, Lebanon (AP) — 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. The health minister said more than 25 people were killed and over 2,500 injured.

There were hundreds of casualties, with bodies buried under the rubble, officials said.

The number of dead was not immediately known, but hours later, ambulances were still carrying away the wounded and officials said Beirut’s hospitals were full. Army helicopters helped battle fires raging at the port.

The cause of the blast was not immediately known.

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.

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 media. Israeli officials usually do not comment on “foreign reports”.

The blast 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 200 kilometres (180 miles) across the Mediterranean.

Read more: Two huge explosions rock Beirut, dozens of casualties