MIFFLINBURG -- An electric water heater exploded in a multi-family dwelling on Market Street early Sunday morning, forcing a number of people out of their homes.

The water heater blew up in the basement on the east side of the building at 424-426 Market St. at about 5:30 a.m., said Mifflinburg Hose Company Chief John Heiges. The building is divided into two sections, with an upstairs and downstairs apartment on the east side and a home on the west side.

The downstairs tenant was home at the time, he said. He could not remember her name, but said she was uninjured, though "she was shaken up pretty bad."

Firefighters searched the house to determine the cause of the explosion, ruling out natural gas because there are no natural gas lines in Mifflinburg, according to the chief.

They quickly realized the water heater was the culprit, but could not find much evidence of the appliance's existence, he said.

"We could not find all the parts of the heater," he said. "We went in to find the cause, gathered a piece or two (of the water heater) and got out. The house was so unstable."

A state police fire marshal from the Milton barracks inspected the scene Sunday, but could not determine what caused the explosion because of a lack of evidence.

"There's no way you're ever going to know," the chief said.

He said the east side of the structure is sagging, and as a precaution, firefighters placed plywood over the windows on the side of the house next door in case the ruined building collapses.

The tenants, along with the homeowner, who lives on the west side of the building, have not been allowed back in because of how unstable it is. He said they are staying with friends or family.

The tenant in the upstairs apartment, Heather Beirly, was not home when the water heater exploded, according to the chief.

He said a structural engineer should be out today to inspect the building "and see whether they can even go in and collect their belongings ... We're not going to let anybody back in until the insurance company decides what they're going to do."

The basement foundation wall separating the two sides of the building was not damaged, he said, and as a result, the west side of the building is more structurally sound.

Firefighters also closed Market Street in front of the structure.

The Mifflinburg Ambulance and New Berlin Fire Company also responded to the scene.