Japan's government has urged people in Tokyo to use less electricity on Monday, as it warned that supplies will be strained as the country faces a heat wave.
Over the weekend, the temperature in central Tokyo went above 35 C, while the city of Isesaki, northwest of the capital, saw a record 40.2 C. That was the highest temperature recorded in June for Japan.
The ministry said that excess capacity for electricity was expected to drop to 3.7% on Monday afternoon in Tokyo and eight surrounding prefectures. It views a buffer of 3% as necessary for stable power supply.
The reserve margin will fall below the minimum required of 3% if demand and sudden supply problems increase, the government asked people to turn off unnecessary lights for three hours from 15: 00 Tokyo time 07: 00 BST while properly using air conditioning and hydrating during hot hours.
The Japanese government called for households and companies to save as much electricity as possible during the summer.
On Sunday afternoon, Japanese public broadcaster NHK reported that 46 people in Tokyo had been taken to hospital for suspected heatstroke.
It also said a 94-year-old man in the nearby Kawagoe city was suspected to have died from the condition.
The news comes after Australian officials have urged households in New South Wales - a state that includes the country's biggest city Sydney - to switch off their lights in the face of an energy crisis.