Tens of thousands left without drinking water and electricity, while thousands sleep in school gymnasiums.
More than a dozen people have died in Tokyo as Japan struggles to cope in record-breaking heat.
Temperatures in Japan are often hot and humid, but the current weather is bringing unprecedented stretches of unrelenting heat.
At least 14 people are known to have died in the Japanese capital alone, with the Philippine television network ABS-CBN reporting that the total number of people who have died since the heatwave began on July 9 has reached 30.
Temperatures in the ancient capital of Kyoto was 38.3 degrees Celsius on Thursday, marking the seventh straight day of 38C or higher heat – a level unseen since record-keeping first began.
The highest recorded temperature in this current heatwave was 40.7C in the central Gifu Prefecture. This was reported on Wednesday, the same day that Tokyo’s temperature surged to 36C.
Tens of thousands of people between the ages of one and 105 have received hospital treatment.
The education ministry is urging schools and universities to take measures to prevent heat stroke after a six-year-old boy died on Tuesday following an outdoor class at his elementary school in Aichi Prefecture, central Japan.
The extreme heat has made it increasingly difficult for the victims of devastating flooding and landslides which smashed western Japan just two weeks ago, destroying nearly 10,000 households in Hiroshima, Okayama and Ehime.
The heatwave is also reviving concerns about the Tokyo 2020 Olympics, which will be held during the summer.
The temperature across much of Japan is expected to be slightly lower over the next two days, before rising again on Monday and Tuesday.