Electrical power began to flow again to parts of the northeast and midwest Friday, as Americans struggled to return to normalcy after a harrowing blackout which struck on Thursday. The outage plunged cities into darkness and stranded thousands of commuters and tourists. Power disruptions which swept through eight states and part of Canada.

Power gradually came back throughout the day Friday, but millions still grappled with the impact of the blackout.

In New York City, the subways remained closed and non-essential workers were told to stay home.

Restaurants gave away or threw away perishable food and stranded tourists slept in the streets and train stations rather than face stifling hotel rooms.

Late Friday, New York Governor George Pataki made another appeal to residents to keep electrical use to a minimum, even as the power continues to come back on.

"We still are in the midst of this crisis," he said. "There are still millions of people in this state who have no power and what we are urging everyone to do is to conserve energy."

Governor Pataki also said he and officials from some of the other states affected want the federal government to find out what caused the cascading blackouts.

New York City Mayor Michael Bloomberg said police and fire officials had been inundated with emergency calls since the blackout began, but he said there was no spike in crime.

Speaking on a local radio station, he also praised the generally calm attitude of New Yorkers

"We will look back on this as a very bad annoyance, but I think New Yorkers conducted themselves in such an extraordinary manner and we will probably look back on this with a smile on our face and realize the difference between how we dealt with this crisis in the year 2003 compared to back in the 1970s when the city fell apart," he said.

Airlines canceled flights in the affected areas and train service between some major cities was slow to return to normal.

Power also slowly returned to the affected areas in the midwest and Canada. Residents of Detroit, Michigan, and Cleveland, Ohio, were urged to boil water for the next few days as a health precaution.

Jane Campbell is the mayor of Cleveland.

"Water is still under the boil alert. That means that when the water begins to flow, you have to, for 24 hours, boil the water four minutes for the first 24 hours," said Jane Campbell, the mayor of Cleveland."

The blackout initially knocked out Cleveland's water pumping stations and local officials said it would take some time for water supplies to return to normal.

Michigan Governor Jennifer Granholm said it may take a few days for all the power to be restored in her state.

She also said that emergency preparedness improvements made in the wake of the 2001 terrorist attacks had made a difference.

"It was September 11, I think, that precipitated the kind of coordination that we are seeing and as a result of that kind of coordination, I think we have mitigated what potentially could have been some very, very serious consequences," she recalled.

In California, President Bush told reporters that the blackouts demonstrate the need to upgrade the nation's electrical power distribution system.

"But we will find out what caused the blackout and we will deal with it," he said. "I view it as a wake-up call. You know, I have been concerned that our infrastructure, the [power] delivery system is old and antiquated, and I think this is an indication of the fact that we need to modernize the electricity grid."

As to the cause of the blackout, the investigation continues. Power officials said it was too early to know for sure what caused the outage but they were focused on a failure in a power distribution route in northern Ohio as the possible trigger for the massive blackout.

At its height, an estimated 50 million people were affected by the loss of power in eight states and Canada, about twice the number affected by a similar blackout in New York and New England in 1965.