(Updates with power to be restored later Friday, quotes, details)
By Grant McCool
NEW YORK, Aug 15 (Reuters) - New Yorkers sweltered in the heat and humidity while waiting for electricity to be fully restored on Friday, but miraculously only one death in the city could be blamed on the worst power failure in North American history, Mayor Michael Bloomberg said.
Bloomberg said at a news conference 17 hours into the massive blackout that he expected electricity to be restored later on Friday and that by the next full business day on Monday the city would be back to normal.
"Power won't be restored to all New Yorkers until later today," said Bloomberg, a businessman-turned-politician who is managing his worst crisis since becoming mayor in January 2002. "I would not expect you to have subway service for the evening rush hour."
The New York Stock Exchange and other financial markets opened, but normal trading was not expected. "There is going to be next to nothing today," one trader said as he entered the exchange.
"I think by Monday everything will be back to normal," Bloomberg told reporters.
Officials said they still did not know what caused the outage on Thursday afternoon that covered parts of Canada and several northeastern states.
With tens of thousands of people milling in the streets, the crisis reminded many New Yorkers of the Sept. 11, 2001 hijacked plane attacks. But officials were quick to reassure the public that the outage was not an act of terrorism.
U.S. power grid operators called it the biggest power failure in North American history, worse than those of November 1965 and July 1977.
The three major New York area airports -- LaGuardia, John F. Kennedy and Newark -- were operating some inward and outward bound flights, officials said.
ONE DEATH
City hospitals reported treating more people than usual for heat exhaustion and heat related ailments.
Bloomberg said only one death could be attributed to the blackout, a 40-year-old woman who died of a heat-related heart attack while evacuating from a building.
Emergency services personnel rescued 800 people from elevators and the number of crimes reported was less than an average night, police said. And the mayor said one firefighter was injured battling a fire.
"In short, New Yorkers showed that the city that burned in very similar circumstances in the 1970s is a very different place," Bloomberg said.
As dawn broke in Times Square, hundreds of tired, haggard-looking commuters left stranded without lodging by the blackout awoke from their makeshift beds of newspaper and cardboard on city sidewalks.
Officials urged commuters from the suburbs and boroughs to stay out of Manhattan unless their work was essential to helping the restoration of power. Utility companies asked customers to conserve energy and restrict use of air conditioners.
With subway train service suspended, some of those who walked out of Manhattan on Thursday evening headed back on foot on Friday.
"Well, why not get a bit of exercise," said John Cole, 47, wearing shorts, T-shirt, sandals and a backpack as he walked off the Brooklyn Bridge headed to work on Wall Street.
Bloomberg told reporters that electricity was returning gradually to all five boroughs in the city of 8 million, the most populous in the United States. Power was restored to much of Times Square on Friday morning, but none of the "super signs" were working, officials said.
"There were thousands of small acts of kindness," said Tim Tompkins, president of the Times Square Business Improvement District. "It was, as it always is, New Yorkers being New Yorkers, in their crazy version of a town square."
Temperatures were expected to soar to 90 degrees Fahrenheit (32 degrees Celsius) with high humidity as on Thursday, forecasters said.
New York Gov. George Pataki said at a Friday news briefing that he and other New Yorkers wanted answers to what caused the blackout.
"I wish we could give you an answer ... part of it depends on the ability of people to conserve power," Pataki said. "There is no question that there is something seriously wrong."