A gas explosion ripped through an apartment building in northeastern Spain before dawn Wednesday, injuring at least 28 people, authorities said.

The blast left gaping holes in the front, sides and roof of the three-story building in Gava, an industrial and farming town southwest of the Catalan capital of Barcelona.

Among the 28 people injured were five children, said Marina Geli, the Catalan regional health minister.

Eighteen of the injured were in serious condition with burns to at least 60 percent of their bodies, and in some cases 90 percent, she said at a news conference.

Firefighters put out flames seen shooting throughout the building’s roof, and they were searching for more possible victims. But officials said they did not expect to find any one else.

Television footage showed curtains and blankets hanging from ruined apartments, while pieces of furniture and electrical appliances littered the area outside.

“We heard a loud explosion and we ran out. The building was completely destroyed,” Juan Exposito, who lives opposite the damaged building, told the digital edition of the Barcelona newspaper La Vanguardia.

Authorities are investigating what might have caused the explosion at 3 a.m. (0200GMT).