An explosion leveled a gas station near a ski resort Tuesday morning, killing at least four people and seriously injuring at least nine others, authorities said.

A firefighter and a paramedic were among the injured at the Flat Top Little General Store on Route 19, said Kim O'Brien, spokeswoman for the state Fire Marshal's office, who provided the casualty figures.

Authorities suspect that a propane tank exploded at about 10:45 a.m., just as a fire truck was pulling into the station in response to a report of a leak.

The cause of the explosion has not been determined. O'Brien said she's not sure whether it was a propane tank or a liquid petroleum tank that exploded.

All that's left of the building is a pile of debris, twisted metal framework and a sign showing the price of gasoline starting at $2.19 a gallon.

The explosion was felt at least a mile away at The Ski Shop.

"I thought we got struck by lightning. The whole building shook. The power went off," said Ben Monast, the shop's manager.