A person wearing face masks to help protect against the spread of the coronavirus walks by a cooling mist spot, June 28, 2022 in Tokyo. (EUGENE HOSHIKO / AP)

TOKYO - The highest temperatures in at least 147 years have scorched much of eastern Japan for a week as of Friday, with the government asking citizens to cut power use as much as possible, while still running air conditioners to stay safe.

The region around Tokyo was set for its seventh straight day of temperatures above 35 Celsius and faced a hot weekend as well, and the western city of Nagoya was predicted to hit a sizzling 40C. Slightly cooler temperatures and possibly rain could bring relief on Monday.

Authorities issued no warning of a possible power crunch for the first time this week, although energy supplies will remain tight amid rising energy prices, adding fervor to calls within the government to restart more nuclear reactors that have been offline since the Fukushima disaster of March 2011.

The Japanese government warned dangerous conditions would persist, again encouraging people to relax the use of masks outdoors, a message slow to take root in Japan, where mask-wearing was popular even before the pandemic

The government warned dangerous conditions would persist, again encouraging people to relax the use of masks outdoors, a message slow to take root in Japan, where mask-wearing was popular even before the pandemic.

"Since it raises the risk of heatstroke, please take off your masks outside if you are far away from others and not speaking," Deputy Chief Cabinet Secretary Seiji Kihara told a news conference.

The power grid in greater Tokyo, home to 37 million people, crept perilously close to usage levels that could have threatened power outages on Thursday. The situation has eased, though, as measures taken by authorities to deal with summer peak demand kicked in with the start of July.

READ MORE: Japan's heatwave sizzles into hottest day, power crunch risk 

Japan frequently sees scorching summer temperatures. Last year, several events at the Tokyo Olympics in late July had to be rescheduled due to the heat. But temperatures in June this year have been unprecedented, catching authorities unprepared.

"Due to the record high temperatures, we had (power) demand nearly equal to summer peak levels in June - before we were able to gather sufficient supply resources. That's why things got tight," an official at the Ministry of Economy, Trade and Industry told reporters on Thursday.

Some manufacturers shortened work hours and some companies asked workers to turn off unused appliances earlier this week. A few commuter train stations also shut off escalators, and an amusement park in Yokohama, a city near Tokyo, turned off the lights on its Ferris wheel and ropeway at night, the Nikkei Shimbun reported.

ALSO READ: Tokyo heatwave worst since 1875 as power supply creaks under strain

The heat came with an early end to the rainy season, which in some parts of Japan lasted barely two weeks, leaving dams partly empty and some areas calling for water conservation.

A tropical storm may brush Japan next week, finally bringing rain and slightly cooler temperatures.