The mercury hit 32 degrees at 7:30 a.m. Sunday in central Tokyo, prompting the Meteorological Agency to issue warnings for high temperatures across much of the nation after at least 11 people died of suspected heatstroke the previous day.

A heat wave that has gripped most of the country for the past week was forecast to continue until at least Thursday, the agency said. Many cities are seeing their highest temperatures ever.

“It’s like a sauna,” said a 50-year-old woman in Tajimi, Gifu Prefecture, where the mercury hit 40.7 degrees Wednesday.

As of 11 a.m., 601 of the agency’s 927 observation spots had recorded temperatures of 30 or higher. Readings over 35 were taken in 57 locations including Tottori, Maebashi in Gunma Prefecture, and Kameyama in Mie.

The Tokyo Fire Department said Sunday that 3,091 ambulances were dispatched in the capital the previous day, the most in a single day since it began emergency medical operations in 1936.

Dispatches have been surging since Tuesday, pushed up by the sweltering heat enveloping the capital, the department said.

Almost all of the 11 victims Saturday were seniors, including two couples in their 70s found dead in their homes in Tokyo and Osaka. According to a Fire and Disaster Management Agency figure, 21 people who were rushed to hospitals died of heatstroke between April 30 and July 15.

The emergency calls Saturday included reports that junior high school and high school students had fallen ill during sports activities in Shizuoka and Ibaraki.

“If you don’t have enough energy, you’re vulnerable to heat exhaustion, which could become serious in a short period of time. It’s important not to skip meals and to get enough sleep,” said Takashi Fukushima, who heads a clinic in Tokyo.

Fukushima added that dizziness could be the first signs of heat exhaustion, which can lead to deadly heat stroke. “If there is something wrong, you may want to suspect heat exhaustion.”