Japan's Fire and Disaster Management Agency says the weekly number of people taken to hospital with heatstroke has doubled in the country from the previous week amid a heat wave.

The agency says 8,189 people were taken to hospital in the week through Sunday.

The number has not just doubled from the previous week, but has also doubled from the same period last year.

During the week, daytime highs topped 39 degrees Celsius in many areas in Japan.

Three people have died.

People aged 65 or over account for more than half of the total with heatstroke, at 4,484.

By prefecture, Tokyo logged the highest number with 1,066. That is 4.6-fold compared with a year earlier.

By location, 3,215 people developed heatstroke at home, while 1,445 people outside on the streets.

The Meteorological Agency says scorching temperatures are expected to continue in many areas for the coming week. Officials are calling on people to use air conditioners, keep hydrated and take a rest from time to time if they work outdoors.