At least 44 people have died and thousands have been taken to hospital in Japan as temperatures hit a record breaking 41.1C.
The high temperature was recorded in the city of Kumagaya in Saitama prefecture.
Japan has been hit by a heatwave with temperatures currently 12 degrees hotter than average temperatures for this time of year.
In Tokyo, more than 3,000 emergency calls were made on Wednesday in response to the heat with 300 people hospitalised.
Meteorological Agency official Minako Sakurai said: “People in areas where temperatures are as high as 35 degrees or higher should be extremely careful”.
“And even at lower temperatures, the heat can be dangerous for small children and elderly people, and depending on the environment and activities you are doing.
“People should be all the more careful as many people must be exhausted after days of cruelly hot weather.”
The recent heatwave has prompted concerns that the Tokyo Olympics in two years time could be braced for sweltering heat.
The 2020 Olympics will run from July 24 to August 9, when temperatures in central Tokyo can exceed 35C.
During a visit to Tokyo earlier this month, John Coates, the head of an International Olympic Committee inspection team, acknowledged the heat will be a huge challenge for organisers.
"We are mindful that we do have to prepare for extreme heat," he said at a news conference. "You're not the first country to host the games in extreme heat. It's a natural consequence of being in July and August."
Mr Coates said organisers should explore all options to combat the extreme heat.
The marathon and a number of other outside sport events will be held early in the morning to avoid scorching heat, a plan approved by the IOC showed.
The flooding was the worst natural disaster in Japan since the earthquake and tsunami of 2011.
