Fireballs and explosions could be seen and heard in downtown Brooklyn yesterday after a fire on the roof of a police station ignited three 100-pound propane gas tanks, Fire Department officials said.

Ten workers tarring the roof when the fire started managed to escape before the propane tanks exploded on the roof of the 84th Precinct at 301 Gold St., fire officials said. The fire spread to the Fire Department’s 31st Battalion building behind the precinct.

A construction worker at a building across Gold Street said the explosion was so powerful it knocked the concrete he had been adding to a window frame into the street. One of the tanks flew several hundred feet in the air and landed near the Brooklyn-Queens Expressway, a police officer at the scene said.

The two-alarm fire officially started at 3:11 p.m. and was under control by 3:45 p.m., according to the Fire Department.

Although fire officials said there did not appear to be any damage to the building, the thick smoke from the burning tar could be seen all around downtown Brooklyn.

About 100 firefighters responded to the scene. One firefighter was hurt when she fell down several stairs, Fire Department officials said. All major thoroughfares in the area were closed until early evening while officers checked the roof for safety.

The precinct, which houses evidence collection and anti-crime units, was evacuated as soon as the fire was reported, police officials said. As of yesterday evening, the building had not been reopened. Police were considering using the Transit Police Academy across the street as a temporary headquarters, officials said.

Police and fire officials said they were investigating the cause of the fire.