Residents of San Juan, Puerto Rico, are at risk of possible smoke inhalation and acid rain due to a raging fire, officials said Saturday.

Officials were concerned a wind shift Saturday could put additional San Juan residents at risk for smoke inhalation and that smoke from a fuel storage facility fire could mix with expected precipitation to create acid rain, CNN reported.

The fire at the Caribbean Petroleum Corp. facility just outside San Juan began with a major explosion Friday. Police said as of Saturday, at least 15 of the 40 fuel storage tanks at the facility were still ablaze.

As firefighters attempted to contain the fire, authorities had hundreds of local residents moved to local shelters as a precaution.

Pedro Nieves, chairman of the Puerto Rico Environmental Quality Board, said steps had been taken to prevent fuel from entering San Juan's nearby bay.

"We have been monitoring the water visually, and we have installed preventive pads and other material to contain a spill," Nieves said. "No oil has reached the water."

CNN said the official cause of the explosion and ensuing fire had not been determined.