Japan started the operation of an upgraded alert system for heat stroke on April 24.

The government has been using a system to alert people of heat stroke since 2021.

The upgraded "Special Heat Stroke Alert system" will issue a warning when "unprecedented heat" could impose higher threat to life.

The warning will be issued after considering factors such as temperature, humidity and wind conditions.

When the warning is issued, designated facilities will be required to open as shelters for heat relief.

The move comes as summer mercuries in the country continue to rise each year.

Weather officials announced last year that average temperatures from June through August 2023 was the highest ever since statistics began in 1898.