TOKYO (AFP) - An "unprecedented" heatwave in Japan has killed at least 65 people in one week, government officials said Tuesday (July 24), with the weather agency now classifying the record-breaking weather as a "natural disaster."

In the week to Sunday at least 65 people died of heat stroke while 22,647 people were hospitalised, the Fire and Disaster Management Agency said in a statement.

Both figures are "the worst-ever for any week during summer" since the agency began recording fatalities resulting from heat stroke in July 2008, an agency spokesman told AFP.

The Fire and Disaster Management Agency said Tuesday that a total of 80 people have died from the heat since the beginning of July, and over 35,000 have been hospitalised.

Among those killed was six-year-old school boy who lost consciousness on his way back from a field trip.

"As a record heatwave continues to blanket the country, urgent measures are required to protect the lives of schoolchildren," top government spokesman Yoshihide Suga told reporters Tuesday.

The government said it would supply funds to ensure all schools are equipped with air conditioners by next summer.

Less than half of Japan's public schools have air conditioning, and the figure is only slightly higher at public kindergartens.

Suga said the government would also consider extending this year's summer school holidays as the heatwave drags on.

On Monday, the city of Kumagaya in Saitama outside Tokyo set a new national heat record, with temperatures hitting 41.1 degree Celsius.

And temperatures over 40 deg C were registered for the first time in Tokyo's metro area, where the government is promoting Uchimizu, a tradition where water is sprinkled onto the ground, as part of a summer heat awareness campaign.

It was marginally cooler on Tuesday, but temperatures remained well above normal in most of the country, and little relief is forecast.

"We are observing unprecedented levels of heat in some areas," weather agency official Motoaki Takekawa said late Monday.

The heatwave "is fatal, and we recognise it as a natural disaster," he told reporters.

The agency warned that much of the country will continue baking in temperatures of 35 degrees or higher until early August.

Officials have urged people to use air conditioning, drink sufficient water and rest often.

Japan's summers are notoriously hot and humid, and hundreds of people die each year from heatstroke, particularly the elderly in the country's ageing society.

The heatwave follows record rainfall that devastated parts of western and central Japan with floods and landslides that killed over 220 people.

And many people in the affected areas are still living in damaged homes or shelters and working outdoors on repairs, putting them at great risk.

The record-breaking weather has revived concerns about the Tokyo 2020 Olympics, which will be held in two years time in July and August.

Tokyo governor Yuriko Koike this week promised that the heat would be given the same priority as measures to counter terrorism.

"It's just as important because the purpose is also to protect people's lives," she told reporters, comparing Japan's summer to "living in a sauna".