An apparent explosion rocked a Hilton hotel under construction Monday and a fire official said a dozen workers were injured.

Two of the injured were in critical condition, eight had serious injuries and two had minor injuries, fire department spokesman Maurice Luque said.

Some workers were burned and others were injured by flying debris, Luque said. The building did not burn, he said.

About four lower floors of the waterfront skyscraper near the San Diego Convention Center showed serious damage and debris littered a driveway beneath the area.

“We don’t know what happened,” Luque said. “We’ve heard all kinds of things. We will know but right now we do not know.”

Firefighters searched the building to determine if there were other victims.

The site was surrounded by firefighters and utility crews, and a truck with the markings of the Bureau of Alcohol, Tobacco, Firearms and Explosives arrived.