A late-afternoon (this morning NZ time) power blackout hit New York City, other parts of New York state and Connecticut, and extended west into the Midwest and north into parts of Canada.
Initial reports suggested that no injuries resulted and there were early signs that the internet had survived the incident without disruption, although cellular networks were clogged in some areas.
New York Governor George Pataki said in a press conference at about 6pm Eastern time that power was beginning to be restored in some areas.
The series of blackouts began at about 4pm Eastern time and there was no immediate indication they were linked to a terrorist act.
"There is no evidence of terrorism whatsoever," said New York City Mayor Michael Bloomberg, at a televised press conference. "There was a power failure in Northern New York or Southern Canada that cascaded down through the system."
"To the best of our knowledge no one has been injured during the evacuations from tall buildings or subways," Bloomberg said. "There are people in the subways but the police say evacuation procedures are working."
The massive blackout left the internet largely untouched, except for certain news websites that were slowed by high volumes of traffic, according to web performance management services company Keynote Systems, in San Mateo, California.
"We see no problems in terms of performance of the internet nationwide. We would not expect any as all the major internet infrastructure providers have data centres with backup generators. They can go for days without commercial power," says Lloyd Taylor, vice president of technology and operations at Keynote Systems.
The "flash crowd" effect that hit news websites such as CNN.com and USAToday.com affected performance of those sites a bit, Taylor says. Availability of the Cable News Network (CNN) site dropped about 5% in the hour after the power outage, and USAToday saw about the same effect, he says.
"The American public is trained to go to the web for breaking news. Most of the major news sites now know how to handle this kind of situation," Taylor says, referring to past instances when news sites have been crippled because of sudden increases in traffic.
The long-distance voice and internet backbone network of MCI continued to operate normally, Linda Laughlin, a spokeswoman for the company, said about two hours after the blackouts began. Some New York switching facilities of MCI, the long-distance and internet backbone provider based in Reston, Virginia, are operating on generator power after automatically switching over when commercial power failed, she said.
Some mobile phone customers were unable to make calls. Multiple cell sites for Sprint PCS Group were affected, which had an impact on PCS customers attempting to call in and out of the area, says Dan Wilinsky, a spokesman for Sprint PCS, a division of Sprint in Overland Park, Kansas, speaking a few hours after the outages began. Wilinsky was not able to give the number or location of the affected sites.
"Because of the tremendous number of calls going into and from the area, we are asking customers not to call unless absolutely necessary," Wilinsky says.
All of Sprint's major switching centres were operating, some on emergency generators, and its internet infrastructure was operating normally, he says.
Mobile phone operator Cingular Wireless saw service affected in Manhattan and Long Island, New York, as well as in Northern New Jersey, Detroit and Cleveland, says Clay Owen, a spokesman for Cingular, in Atlanta.
"We do have battery backup at our cell sites as well as power generators at the switches, but cell services were interrupted," he says.
Call volumes were still extremely high in the affected areas a few hours after the outages began. Cingular asked customers in those areas to use their phones only for emergency calls to avoid further overloading the network, Owen says.
Verizon Wireless' network was operating with some cell sites and switches on emergency generators, according to a company statement. The carrier reported heavier than normal call volumes and advised customers who couldn't get through to wait several minutes before attempting to redial.
Technicians from Nextel Communications, which operates mobile phone networks in most of the affected metropolitan areas in the US, were monitoring the situation, says spokeswoman Elizabeth Renz, in Reston, Virginia.
"This is a real-time situation and it's too early to determine any customer impact," Renz says.
New York Governor George Pataki declared a state of emergency across the state. People were advised to walk home and avoid driving their cars.
TV and radio reports indicated that people were trapped in elevators and traffic was snarled in numerous parts of the Northeast
Aircraft bound for New York City were being diverted to other airports, including those in Boston and in Bangor, Maine. New York Mayor Michael Bloomberg announced at about 5.50pm that power was starting to return in some areas and said restoring electricity would take "hours, not minutes."
Streets in Manhattan were packed on Thursday evening, with many people going home on foot. Long lines formed at pay phones as cellphone users had trouble getting calls through. Traffic signals were dark and police were directing traffic.
"It's mayhem," says Santos Diaz, who works at a travel wholesaler Travel Bound, in lower Manhattan. Diaz was outside Travel Bound's office with his wife, Jackie, who works at the same office. They were trying to figure out how to get home to Long Island.
"At first everyone thought it was an attack," but battery-powered radios in the office soon provided the real story, Diaz says.
At least two technology companies in the area were affected. Generators restored power at IBM's Armonk, New York, headquarters shortly after commercial power went down, IBM spokesman Brian Doyle says. IBM has generators in place in many of its locations, so the company and its customers should not be affected by the outage, he says.
"We have backup systems in place that are operating as planned," Doyle says.
Even though the generators are running, IBM told staff at its headquarters and other nearby locations that they could go home. "We made an announcement that there is this massive East Coast power outage and that, by the way, the gates at the entrances have been raised, allowing them to leave."
Sun Microsystems says 15 of its offices were hit by the blackout, including those in New York City and Toronto. Most were sales offices and about a thousand staff were affected, says Sun spokeswoman May Goh Petry.
Customers with Sun equipment who were hit by the blackout could call Sun for advice and Sun was ready to provide replacement components where needed, although it was too early Thursday evening to assess any damage that may have been caused, she says.
"Different customers have different service level agreements, so it depends partly on that, but right now I think everybody's just trying to figure out what's going on," she says.
The CERT Coordination Center in Pittsburgh said there is no indication that the outage is related to this week's W32/Blaster worm.
The list of cities affected included Cleveland and Hartford. Some parts of several states were also hit, including Pennsylvania, Kentucky, Tennesee and New Jersey.
(Additional reporting by Martyn Williams in Tokyo, Joris Evers and James Niccolai in San Francisco and Stacy Cowley in New York.)