Extreme temperatures forecast for capital this week after premature end to rainy season

Temperatures of 35C were forecast in Tokyo for Monday as the capital battles record June temperatures. Photograph: Xinhua/REX/Shutterstock

Japan’s government has warned millions of people in the Tokyo region to save energy or face power cuts, as the capital battles record June temperatures after a premature end to the rainy season.

Temperatures of 35C (95F) were forecast in the city throughout the day, with similarly extreme weather expected for the rest of the week, according to the Japanese meteorological agency.

“We ask the public to reduce energy consumption during the early evening hours when the reserve ratio falls,” Yoshihiko Isozaki, the deputy chief cabinet secretary, told reporters.

Isozaki advised households and businesses to turn off lights not in use and limit air conditioner use, although he added that people should guard against heatstroke.

The economy and industry ministry said people living in the region serviced by Tokyo Electric Power [Tepco] should conserve energy, especially when demand peaks in the late afternoon and early evening. Reports said reserve generating capacity risked dropping as low as 3.7% in Tokyo and the surrounding region at that time; below 3% risks power shortages and blackouts.

Kaname Ogawa, the director of electricity supply policy at the ministry, said electricity demand was higher than expected because the temperature had exceeded Sunday’s forecast. “We are struck by unusual heat for the season,” Ogawa said. “Please cooperate and save as much power as possible.”

Much of Japan would normally be experiencing less uncomfortable temperatures during the middle of the rainy season. But on Monday, the agency declared the season had ended – the earliest date on record – in the Kanto region, which includes Tokyo.

It was the earliest end to the season since records began in 1951 and 22 days earlier than usual.

The heat has hit other parts of the country in recent days. On Sunday, Isesaki city in Gunma prefecture, north of Tokyo, recorded the country’s highest temperature in June, at 40.2C.

More than 250 people were taken to hospitals in the capital over the weekend after suffering heatstroke, according to the Mainichi Shimbun newspaper.

“Immediately after the rainy season ends, many people are yet to be fully acclimated to heat and face a greater risk of heatstroke,” the meteorological agency said in a statement.

Officials have been encouraging people to remove their masks when outside to prevent heatstroke, although many were still wearing face coverings in Tokyo on Monday.

Asako Naruse, who was out sightseeing in the city, said she had never experienced such brutal heat this early in the summer. “I’m from northern Japan, so these temperatures seem really extreme,” she said.