Temperatures rose across Japan on Saturday to highs usually not seen until the height of summer, causing hundreds of people to be taken to hospitals and prompting the weather agency to issue heatstroke warnings.

The city of Taketa in Oita Prefecture, southwestern Japan, marked 35.0 C, the hottest in the country this year, while more than 420 monitoring spots, including those in central Tokyo, Nagoya, Osaka and Fukuoka, all saw the mercury rise above 30.0 C.

The number of people taken by ambulance to hospitals to be treated for heat-related illness reached at least 460 across the country, according to data compiled by Kyodo News.

The unusual heatwave is expected to continue through Monday in many parts of Japan, according to the Japan Meteorological Agency.

Other cities including Aomori, Nara, Matsuyama and Yamaguchi marked record-high temperatures for the month of May.

More than 95,000 people were taken by ambulance to hospitals to be treated for heatstroke between May and September last year, a record-high amid a heatwave so severe that it was designated a natural disaster by the government.