On what may have been the final day of the latest heat wave, power outages were reported at hundreds of locations across the five boroughs, affecting thousands of people who were then unable to turn on their air-conditioners or get much-needed ice from their freezers. The city’s first heat-related death was also reported — an unidentified man in Brooklyn who the mayor said may have been drinking.

Meanwhile, three elderly people were found dead in Hempstead, L.I., last night, police sources said. They had no air-conditioning in their living space, the sources said.

On Manhattan’s East Side at about 7 a.m., there was an explosion under a manhole cover outside the Medical Examiner’s Office that sent several doctors scurrying to the office’s Queens branch with four corpses scheduled for autopsy.

“There was fire and an explosion,” the spokeswoman for the office, Ellen Borakove, said. In front of the building, Consolidated Edison workers ripped up part of the street and brought in heavy machinery to repair what appeared to be a burnt-out transformer.

The Medical Examiner’s Office and the neighboring New York University Medical Center and Bellevue Hospital powered their buildings with emergency generators, as did hotels, apartment buildings, and small businesses in the area. They were responding to requests from local politicians and Con Ed to shut down power while the repairs were made.

Although Con Ed officials said they had the situation under control, one worker, who had been repairing the system for about 14 hours already by early yesterday afternoon, said the city’s power problems were the worst he’d seen in his 17-year career with the company. He asked that he not be identified because he wasn’t authorized to speak to the press.

A spokeswoman for Con Ed, Elizabeth Clark, said it was the community’s quick response to the company’s requests that helped it get some of the power restored to East Side neighborhoods later in the day. Four of 24 feeder cables to the Madison Square electrical networks went down in the morning, and two were repaired by the afternoon, she said. Three of the 12 feeder cables in the Kips Bay network, which includes Con Edison’s headquarters near Union Square, went down as well. The building used a backup generator to take pressure off the system, Ms. Clark said.

With fear of a blackout running high among New Yorkers, the atmosphere was ripe with rumors. One took the form of a rapidly circulating e-mail that was forwarded around to perhaps thousands of New Yorkers in the early afternoon. Written in several variations, it was purportedly authored by a person who claimed that her friend’s father was a Con Ed employee who had inside information about an imminent blackout.

A meteorologist at the National Weather Service, Dennis Feltgen, said the highest temperature occurred at La Guardia Airport at 3:49 p.m., when the mercury hit 100 degrees. With the humidity, it felt more like 110 degrees at times during the day, he said.

In what perhaps crystallized just how delicate the power grid has been during the week’s heat wave, Mayor Bloomberg joked that appealing to higher powers was not an effort wasted.

In front of a crowd of about 1,000 people at a church in East New York, where he was breaking ground on a new affordable housing project, the mayor spoke after the Reverend Johnny Youngblood and said that he was “hoping the bishop would mention the electric distribution network in his prayer.”

Later in the day, Mr. Bloomberg offered one more appeal to New Yorkers to conserve power as the city moved into what was expected to be the final stretch of the brutal heat.

“Let me stress once again: With the grid under so much stress it really is vital that we do what we can to conserve energy to avoid interruptions in the delivery of electricity,” he said. “The finish line really is in sight.”

The fire department’s paramedics experienced their sixth busiest day in the city’s history. Their office received 4,063 calls between midnight Tuesday and midnight Wednesday, an increase of 20% over last year. The city also used 300 million gallons more water than normal, which was largely due to more than 3,000 fire hydrants being opened illegally. In city housing 289 of the 3,316 elevators were out because Con Ed reduced power, officials said.

Several business owners across the East Side said they were losing thousands of dollars because of the outages.

The owner of the Deauville Hotel on East 29th Street, Mel Freilich, said some of his customers canceled reservations and others were moving hotels. He lost about $10,000, he said.

Around the corner, on Park Avenue at the Clarion Hotel, the general manager, Rushin Gandhi, said Con Ed officials threatened to shut off his power with the help of the police if he didn’t comply with their requests. He did, and said he will lose about $5,000 because of canceled reservations and guests who move out.

“The guests are surprised that such a thing would happen in New York City,” he said.

An assistant manager at Manhattan Fruitier, which had lost its power for the second day in a row, Sarah Palmer, said it was hard to get angry with the Con Ed workers breaking their backs to get power back on.

“We see these guys covered in sweat,” she said. “They’re really working. It’s hard to get mad at them, but it’s disappointing to throw thousands of dollars of merchandise.”

The president of Manhattan, Scott Stringer, said after a meeting with the Office of Emergency Management that this summer’s blackouts are a symptom of a system unable to handle the city’s power load.

“We didn’t learn from the last blackout,” he said. “We’re going to be back next August with hot temperatures and an infrastructure that can’t sustain the power usage. Make no mistake: This is not going to end today.”