Canadian officials insisted a massive blackout Thursday across the Northeast and parts of Canada originated in the United States, though US power workers denied that and American officials blamed Canada.

In the hours of confusion after the outage — the biggest in US history — Canada's government offered conflicting explanations for the blackout, blaming it first on lightning in Niagara, then a fire at a Niagara plant, and next a fire at a Pennsylvania nuclear power plant.

Canada's defense minister, John McCallum, later backed off some of those theories, though remained firm that the source of the problem was in the US section of the intricate power grid shared by the northeastern United States and Ontario.

"The source is an outage in a northeastern United States power plant," said McCallum's spokesman Shane Diaczuk.

In the United States, officials were looking at a power transmission problem from Canada as the most likely cause of the outage, said a spokeswoman for New York Gov. George Pataki. There was no sign of terrorism, officials in New York and Washington agreed.

The outage blacked out much of Ontario, but authorities said the power was starting to return to some areas Thursday night. In Ottawa, the capital, a few packs of youths roamed the streets, and at least five incidents of smashed store windows and stolen merchandise were reported, said police Staff Sgt. Pat Flanagan.

The changing theories started several hours after the power went out about 4:15 p.m. EDT.

Jim Munson, a spokesman for Canadian Prime Minister Jean Chretien said: "We have been informed that lightning struck a power plant in the Niagara region on the US side." The premier's office later said a fire at the Niagara plant in New York caused the blackout, while the defense minister said the fire was at a Pennsylvania nuclear plant.

"That is absolutely not true," said Pennsylvania Emergency Management Agency spokeswoman Maria Smith. "It's bizarre. We have a direct line to each of our five (nuclear) power plants and they are all running at 100 percent ... There's not even a trash can fire, we would know."

Brian Warner of the New York Power Authority said he wasn't sure where the power failure originated.

"The New York Power Authority's Niagara Power Project has at no time during this incident ceased to operate. We also have not experienced a lightning strike at that facility," he said.

An Associated Press reporter in Niagara said the plant was running and that lights were on. A plant employee emerged to speak to the media and to deny any lightning incident.

"That type of equipment failure, we would have known about right off the bat," said Joanne Willmott, a spokeswoman for the New York Power Authority.

In one of the largest previous blackouts, the blame eventually fell on the Canadian side.

On Nov. 9, 1965, a blackout struck the Northeast and parts of Canada, leaving 30 million people in the dark. It took six days for investigators to find the cause: a single faulty relay at the Sir Adam Beck Station no. 2 in Ontario, which caused a key transmission line to disconnect, according to the Blackout History Project, a Web site published by the Center for History and New Media at George Mason University.

In his comments Thursday, the defense minister did not name the plant in Pennsylvania where he believed there was a fire or give further details. But his spokesman later said that McCallum and other Canadian officials were getting their information from a variety of sources, including some in the United States, as the situation unfolded.

In Canada, blackouts were reported in Toronto, as well as Ottawa in the province's eastern reaches and in much of Ontario.

Ontario Premier Ernie Eves declared a state of emergency for the province and asked any nonessential or non-emergency workers to stay home on Friday.

In Sudbury, Ontario, 210 miles north of Toronto, more than 100 miners at a Falconbridge nickel mine were staying in underground lunchrooms because the outage halted elevators to bring them to the surface.

"I wouldn't call it an emergency situation right now — they've got plenty of water, and the ventilation is still operational with the backup power," Sudbury police Staff Sgt. Al Asunmaa said.

Power was also knocked out on Parliament Hill, leaving scant emergency lighting.

In Toronto, streetcars preparing to transport workers around downtown for the evening rush hour ground to a halt, sending riders into the street to hail taxi cabs.

Diane Grover, spokeswoman for the Canadian defense department, said Canada "considers this an act of nature in the Niagara region on the US side of the border."

Grover said the power company, Ontario Hydro, was in the process of separating itself from the American power grid in order to restore electricity to its customers.

Toronto's international airport was one of six in Canada and the United States that temporarily halted flights.

Millions of Canadians were without power, and the total blackout area covered roughly 50 million people. Electricity was out in a broad swath of the Northeast — stretching west to Ohio and Michigan — and in southern Canadian cities, starting shortly after 4 p.m. EDT.

In Toronto, Canada's largest city with more than 2 million residents, traffic snarled at major intersections as workers denied transportation tried to get home in their own vehicles, in taxis or on foot.

Power began to come back in some cities as afternoon turned to evening, but officials said full restoration would take much longer. The Toronto Stock Exchange said it would open as usual Friday, running on backup power if necessary.

(China Daily August 15, 2003)