A huge explosion rocked the Lebanese capital Beirut on Tuesday, killing at least 27 people and injuring over 2,500, according to the country’s health minister until preparing this news.

The blast shook buildings, shattered windows, sent a huge plume of smoke into the sky and left a wide swath of destruction across the city. There were thousands of casualties, with bodies buried under the rubble, officials said.

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 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-colored cloud over the site after the explosion. Orange clouds of toxic nitrogen dioxide gas often accompany an explosion involving nitrates.