NEW YORK, Aug. 14 (UPI) -- The biggest power outage in U.S. history hit cities in the northeastern United States and southeastern Canada Thursday, halting subways and some air traffic.
Among the major cities affected were New York, Boston, Cleveland and Detroit, and in Canada, Toronto and Ottawa. The outage stretched as far west as Lansing, Mich. The outage affected an estimated 50 million people.
New York Mayor Michael Bloomberg said the outage appeared to result from a power grid fault that started in Hamilton, Ontario. CNN reported a transformer fire in Lower Manhattan as well but Bloomberg said the smoke seen at the site was what happens normally when a transformer shuts down. Other reports said the outage began in Ohio.
University of Illinois engineering professor George Gross told ABC what is known as the "eastern grid," which runs on direct current and stretches as far as the Rockies, apparently was affected. The other three power grids -- the western, Texas and Quebec -- were not involved.
Restoring power was expected to take hours.
"The problem is when these power plants went off line, they get cold," Michael Gent of the North American Electric Reliability Council told CNN. "The ones that use natural gas can be back in an hour or so, the ones that burn coal might take four to eight hours, the (nine) nuclear plants might take half a day. This is a very complex and technical issue to bring these plants back up. But we're up to the task."
"It all happened in about nine seconds," he said. He said the outage was not supposed to happen and officials would have to investigate to determine why the outage occurred. Rescue workers helped sweaty commuters out of darkened subways in New York. By 8:30 p.m. EDT, transit officials said everyone had been evacuated and it would take eight hours to bring the system back. It was unclear whether trains would be running again in time for rush hour.
Thousands streamed across the Brooklyn Bridge on foot.
Federal aviation officials said air traffic was halted for a time at airports in New York, Cleveland, Detroit, Toronto and Ottawa. Planes already in the air were being allowed to land but no planes were being allowed to take off from those airports. The restrictions were lifted at LaGuardia and JFK in New York late in the evening.
President Bush called for modernization of the power grid to prevent future incidents.
"This is going to be an interesting lesson for our country," Bush said, adding, "We will find out why (this happened) and we will deal with it."