Japan has recorded its hottest summer on record after a sweltering three months marked by thousands of instances of “extreme heat”, with meteorologists warning that unseasonably high temperatures will continue through the autumn.

The average temperature in June, July and August was 1.76C higher than the average recorded between 1991 and 2020, the Japan meteorological agency said, according to Kyodo news agency.

It was the hottest summer since comparable records were first kept in 1898 and tied the record set in 2023, the agency said. Japan has recorded 8,821 instances of “extreme heat” – a temperature of 35C or higher – so far this year, easily beating the previous record of 6,692 set in 2023, it added.

The brutal heat was not confined to Japan. Swathes of China logged the hottest August on record, the weather service said.

The hot weather prompted delays to the start of the new school year in some Chinese cities. State media reported on Tuesday that some schools and universities in Jiangxi, Chongqing, and Sichuan provinces had pushed the return to school out to 9 September, citing high temperatures.

China Daily said Chongqing authorities had extended school holidays for all kindergarten, primary and secondary schools, and at least a dozen colleges and universities, “to ensure the safety and health of teachers and students amid the extreme heat”.

Chongqing is notoriously hot in summer, but it and other nearby regions including Sichuan have had abnormally high temperatures in recent weeks. A red alert for temperatures exceeding 40 C – the highest of China’s three-tier warning system – was issued for 12 consecutive days from late August until the start of September.

China is the leading emitter of the greenhouse gases that scientists say are driving global climate change.

Beijing has pledged to bring carbon dioxide emissions to a peak by 2030 and to net zero by 2060.

Its weather service said in an article published on Sunday that average air temperatures for August in eight provinces, regions and cities “ranked the hottest for the same period” since records began.

They included the megacity of Shanghai, and the provinces of Jiangsu, Hebei, Hainan, Jilin, Liaoning and Shandong as well as the north-west region of Xinjiang, the weather service said.

A further five provinces chalked up their second-hottest August, while seven more endured their third-hottest.

“Looking back at the past month, most parts of China have experienced a hotter summer than in previous years,” the weather service said.

The major population centres of Shanghai, Hangzhou and Chongqing also saw more “high temperature days” – typically declared when the mercury breaches 35C – than in any August since records began.

Although the heat is expected to recede across much of the north as autumn begins, “it is still too early to end completely”, the weather service said.

Climate scientists have already predicted that 2024 will be the hottest year on record for the Earth because of a warming planet.

The Copernicus Climate Change Service (C3S) said July was the second warmest on record books going back to 1940, only slightly cooler than July 2023.

Extreme heat has seared much of east Asia this summer.

“Throughout the summer, warm air tended to cover the entire country, and from July to August, a Pacific high pressure system mainly covered western Japan, resulting in clear skies and strong sunlight. As a result, the average temperature during the summer was very high nationwide,” the meteorological agency said, according to the Japan Times.

More than 70,000 people were taken to hospital by ambulance suffering from heatstroke between early July and late August in Japan, while consumer spending surged on items such as air conditioners, sweet food and drinks.

Rising global temperatures make extreme weather more frequent and intense, and China has had a summer of extreme weather, from heatwaves across much of the north and west to devastating floods in central and southern regions.

Agence France-Presse contributed to this report