A powerful explosion destroyed a fireworks factory and a nearby electronics plant south of Manila on Thursday, killing at least six people and injuring more than 40, officials said.

The cause of the explosion was not immediately established, but police suspected it was an accident, regional police Chief Perfecto Palad said.

The blast turned an industrial zone 31 miles south of Manila into a smoldering wasteland and gouged out a crater the size of a school bus, witnesses said.

Part of the roof of the Starmaker fireworks factory landed more than a mile away. Unexploded fireworks rained down in the area and shock waves shattered windows, knocked out electricity and toppled concrete walls, said army Col. Romeo Ucag, who responded with his men.

At least 45 people were treated for cuts and injuries at three hospitals, including a man and a woman with severe burns, hospital staff said.

The mutilated bodies of two men and a woman were recovered outside the factory compound in Trece Martires city, police Chief Reynaldo Galang told DZMM radio. Three other people also died, a police spokesman said.

The victims were not immediately identified, police said.

Amid the rubble and smoke, a Roman Catholic priest prayed over the remains of the victims.

Police said about 40 employees were in the fireworks factory at the time of the blast.

An electronics plant in the same compound also was destroyed, said Jennifer Buenviaje, one of the 45 workers who escaped from that factory.

"The first blast was really so loud. Other explosions followed nonstop," she said.

The fireworks factory opened in 1995 and pioneered synchronized music and pyrotechnics in the country.