A continuing heat wave in Japan has led to temperatures as high as 40C, with the casualties climbing up as more deaths were reported.

Public broadcaster NHK reported that until Friday a number of people had been taken to hospital due to heat stroke related symptoms.

The death toll had climbed to 30, after 10 more deaths were reported on Thursday.

A block of ice is placed at a pedestrian street to cool down the spot in Tokyo. Picture: AAP (AAP)

Children play at a water fountain set up at a park in Nagoya. Picture: AAP (AAP)

Some areas in central Japan registered record high temperatures of 40C, said the Japan Meteorological Agency.

On Friday, temperatures had reached a little above 35C, with the heatwave set to continue over the next few days.

The Tokyo Fire Department reported that, rescue teams Thursday responded to more than 3000 emergency calls as the temperatures soared to 40C and 317 people were taken to hospital.

Students involved in outdoor activities across the country were also affected by the rising temperatures and some were taken to hospital after they showed symptoms of heat stroke and exhaustion.

An aerial photo shows ambulances taking students to a hospital due to suspicion of heatstroke at Oizumisakura high school in Nerima Ward, Tokyo. Picture: AAP (AAP)

A high school student and other stand at a mist spray point for cooling while the maximum temperature exceeds 40 degrees Celsius in Tajimi City, Gifu Prefecture. Picture: AAP (AAP)

A six-year-old child died on Tuesday after participating in an outdoor class in school, which led the education ministry to urge educational institutions across the country to adopt preventive measures.

West Japan, still grappling with the devastating effects of torrential rains in the beginning of July, has now been hit by the high temperatures, which are hampering rescue and reconstruction efforts.

High temperatures also caused flight delays on Wednesday from Tokyo's Haneda airport after one of the runway's floor weakened due to heat and caved in, the Japanese transport ministry said.