San Juan, Puerto Rico - Police evacuated part of the Puerto Rican capital San Juan on Friday after an explosion at a fuel storage facility sparked a huge fire.

The explosion - which was heard in a radius of several kilometres - brought down roofs and broke window panes. The subsequent fire was still burning many hours later, while a huge black cloud hung over much of the city.

No one was reported seriously injured, but the authorities were busy evacuating the area, including many homes and a prison that holds 1,700 inmates.

The cause of the initial explosion was not immediately known. The authorities noted that it might take days to put out the fire, which affected more than 10 tanks holding petrol and other types of fuel.

Puerto Rican Governor Luis Fortuno and the mayors of the municipalities affected by the fire advised residents to stay at home and free streets for the use of emergency vehicles.

School lessons and other activities were cancelled in the area close to the site of the fire. (dpa)