The blast shook the town of Kincardine, 130 miles northwest of Toronto, around 11 p.m. last Thursday. Ontario Provincial Police Sgt. Paul Bradley told the Kincardine News the 911 emergency system was swamped.

"We had calls about windows rattling and houses shaking," Bradley said. "It was almost a surreal experience -- there were so many calls coming in."

Many residents were concerned something had gone wrong at the nearby Bruce Power nuclear power plant but officials there said nothing had happened, the Toronto Star reported.

Others speculated it had been sonic booms from a jet but Bradley told the newspaper air traffic controllers said there had been no supersonic craft in the area at the time. Some residents said there was a meteor shower at that time but Bradley said a 12-mile search found nothing.

"We can't confirm or deny anything. We have no explanation," Bradley told the Star.