Seattle ? An explosion at a foundry in Tacoma was still burning Saturday evening, and firefighters were working to cool additional tanks so that they did not also blow up.

The blast occurred at the Atlas Foundry at 3 p.m., and firefighters arrived shortly after to find that a tanker truck that was delivering propane had exploded. An additional propane tank on-site also caught fire, according to Dan Crotty, assistant fire chief at the Tacoma Fire Department.

Trooper Brandy Kessler of the State Patrol said two people have been sent to the hospital with burns, and the driver of the propane truck is unaccounted for. She said the driver did not work for the foundry. The Associated Press was reporting that three people had been taken to the hospital.

Witnesses miles away felt the explosions and saw flames shoot up as much as 1,000 feet. A Tacoma police officer, who happened to be nearby, said, “It looked like the atom bomb, like the mushroom cloud.”

The explosion shut down Highway 16, which has been closed from Interstate 5 to Union Avenue since about 3 p.m., Kessler said. Crotty said a perimeter around the foundry had been evacuated.