HUMMELSTOWN (AP) _ A ruptured gas line caused an explosion that completely leveled a vacant restaurant building Wednesday, causing a fire that took hours to extinguish, yet no serious injuries were reported.

Hummelstown Fire Chief Charlie Cogan said three people were taken away by ambulances; all were treated and released at a hospital. A fourth person arrived at a hospital by private vehicle, Cogan said; he believed that person only had minor injuries.

Cogan said it was amazing that no one was seriously hurt.

"We're trying to figure that out ourselves," he said.

Work was being done on curbs and sidewalks in the area and the explosion happened Wednesday afternoon when a backhoe operator hit a gas line.

Cogan said it helped matters that workers were behind a dump truck, which shielded them from flying debris.

Dozens of fire trucks responded to the three-alarm blaze, which took well over two hours to extinguish once the gas was turned off, Cogan said. Some nearby buildings were damaged by the blast, but no other fires were reported.

Hours later, there was only some steel framing still standing. Cinder blocks, appliances, lumber and other debris had been bulldozed into a pile.

A fire marshal was to return Thursday to finish the investigation, Cogan said.

Hummelstown is about 9 miles east of Harrisburg, the state capital, and 85 miles west-northwest of Philadelphia.