An explosion at a Gulf gasoline facility Friday rocked a neighborhood outside Puerto Rico's capital, causing minor injuries and forcing evacuations as firefighters raced to prevent additional blasts.

Several columns of black smoke and flames were rising from the Caribbean Petroleum Corp., a gasoline warehouse and distribution center on San Juan's bay that owns the Gulf brand in this U.S. Caribbean territory.

FBI agents on the scene were among those investigating what caused the blast, which struck around 12:30 a.m. (0430 GMT), according to police chief Jose Figueroa Sancha.

A police helicopter that flew over the area confirmed that 11 of more than 30 tanks had exploded, Figueroa Sancha said. Firefighters were planning to chill the remaining tanks in an effort to keep them from exploding. Dozens of fuel trucks were also being moved from the area.

"This is about containment," firefighter Brenda Rodriguez said.

The fuel company told authorities that all of its employees who were at the plant are safe, Rodriguez said.

Some people who were driving through the area were injured when the explosion shattered their car windows. One of them, truck driver Alredro Nevares, had cuts on his face from a broken windshield, according to his son Luis.

Federal Aviation Administration spokeswoman Kathleen Bergen said the agency put a temporary flight restriction in place over the area because of smoke.

The flames, which could be seen from miles away, intensified several hours after the explosion and Figueroa Sancha said it would likely take several days to put out the fire.

Authorities were evacuating people from communities downwind from the thick smoke. About 80 people living in a secure facility for Justice Department witnesses were also moved elsewhere, according to attorney general Antonio Sagardia.

Police cars were clearing the way for ambulances and fire trucks arriving on the scene in Catano, across the bay from San Juan, where the blast tore up a highway. Gov. Luis Fortuno urged islanders to stay away from the site to keep the access clear and nearby schools announced they would be closed Friday.

Environmental authorities urged nearby residents to keep their windows shut to avoid potentially dangerous smoke.