Milwaukee ? An explosion that may have started in a large propane tank flattened an industrial warehouse near downtown Milwaukee on Wednesday, killing at least three people and injuring 46 others, authorities said.

The fiery blast at the Falk Corp. factory flipped cars, hurled debris into the air and forced the evacuation of dozens of workers at the plant, which makes large industrial gears and couplings. Burning rubble was spread over several blocks.

“It sounded like when I was in Vietnam, incoming mortar rounds,” said worker David L. Mays, 61, who said the blast knocked him down and turned over his car.

Fire officials had not determined the cause of the blast, but Mays said the company began to evacuate workers after a leak occurred in one of six large propane tanks. He said he and others were outside when one of the tanks blew up.

Firefighters searched through wreckage for hours before accounting for the plant’s more than 700 workers.

“Had they not been evacuating the employees that were in that building, the death toll would have been much higher,” Police Chief Nan Hegerty said.

As many as 120 firefighters and paramedics responded to the fire, along with hazardous materials crews. The flames were extinguished within three hours.

The explosion destroyed Falk’s warehouse and numerous cars and damaged several other buildings in the complex, fire Lt. Brian O’Connor said, adding that the blast could be felt at a firehouse about a mile and a half away.