The Japan Times reports that more than 10,000 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.
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.