TOKYO — Japan is enduring one of its worst heat waves on record, raising concern about potential power shortages amid surging demand, even as officials urged people to keep their air-conditioners running to ward off heat stroke.

In Tokyo on Saturday, temperatures exceeded 95 degrees for the eighth straight day, a streak the capital has seen only once before since 1875, when record-keeping began. Scorching heat has descended on cities across Japan, like Isesaki in Gunma Prefecture, which passed the 104-degree mark on Friday, nearly breaking a record set only two years ago.

A number of deaths have been attributed to the heat, as well as a surge in people being treated for heat stroke and exhaustion. Over 4,500 people with such symptoms were taken to hospitals in ambulances in recent days, more than four times the number from the same period a year ago, according to Japan’s Fire and Disaster Management Agency.

Most of those patients were 65 or older. Senior citizens, who are particularly vulnerable to extreme heat, make up a disproportionate share of Japan’s aging population.

The authorities have been issuing daily heat alerts for a week, asking people to stay indoors as much as possible and to use umbrellas to protect themselves from the sun. Officials have also urged people not to wear face masks, which most residents of Japan have used scrupulously throughout the Covid pandemic, in many outdoor situations.

“I’d like to ask people to take their masks off when walking, jogging and cycling to work,” Seiji Kihara, the deputy cabinet secretary, said on Friday.

Power companies have warned that the heat wave would put the grid under strain, though there had been no outages as of Saturday. Tohoku Electric Power Company, which serves six prefectures in northern Japan, said this week that it would be “extremely difficult” to keep electricity flowing for all of its customers. “Please save as much power as possible,” the company said.

Prime Minister Fumio Kishida and other officials have urged people to keep their air-conditioning on for their own safety, but to cut back on other uses of power. “Most of the lights in my office are off,” Yuriko Koike, the governor of Tokyo, said at a news conference on Friday. “It’s dark.”

Ms. Koike suggested setting refrigerators to higher temperatures and switching off the heated toilet seats that are popular in Japan. (“Under these circumstances, you can completely turn it off,” she said.)

Japan is vulnerable to power blackouts in periods of high demand because it relies heavily on liquefied natural gas, which is hard to stockpile, and which has become more expensive since Russia invaded Ukraine in February. Japan has kept most of its nuclear power plants closed since the 2011 meltdown in Fukushima, and it has been shutting coal-fired power plants to reduce its carbon emissions.

Japan’s Ministry of Economy said on Friday that the heat wave was likely to ease up soon, along with the pressure on the electricity supply. “The heat is expected to be reduced next week, and the power demand will also be less,” it said in a statement.

On Twitter, some people said they were finding ways to cope. Yoko Koguchi, a Tokyo politician, said her daughter’s catchball practice had been canceled because of the heat. “Thanks to this spare time, we are off to a bookstore and a short trip for something delicious,” she said. “I heard a parasol was effective so we are using a large one.”

Others focused on urging people to take care of themselves. “You can’t manage the heat just with your endurance. No matter how tough a person you are, you could lose your life,” said Kentaro Araki, a researcher at the Japan Meteorological Agency. “Please take every possible measure to protect your life.”