Nine people died from heatstroke, including an 84-year-old man and a teenage boy who had been taken to hospital two days ago in Tokyo, Kyodo News agency reported. Three others died from heatstroke Wednesday, it said. Many were hospitalized.

Tokyo Electrical Power Co. warned of a power shortage as people turned up air conditioners.

The company has been firing up old thermal power stations and buying electricity from rivals after a strong earthquake in mid-July ravaged its largest nuclear power reactor, reducing its electricity output by more than 10 percent.

Across the country, vacationers sought refuge indoors at the height of the summer holidays.

Rail tracks were bent out of shape in the sun, and authorities struggled to deal with fire alarms set off by rising temperatures, according to news reports.