Blazing hot temperatures were recorded across a wide swath of Japan from the Tohoku to Kyushu regions on Monday, with the mercury topping 38 degrees Celsius in parts of the Kanto and Tokai areas.

People were advised to remain vigilant and stay indoors whenever possible as the country marked Marine Day, a national holiday, after the government issued heatstroke alerts in 32 of the nation’s 47 prefectures, affecting tens of millions of people.

The figure was the largest yet for a single day this year, local media reported.