A 74-year-old woman collapsed while working in a greenhouse in the eastern prefecture of Chiba yesterday and was later pronounced dead.
In Ibaraki, also in the east of the country, a 61-year-old was found collapsed in her garden and died.
Today, a 76-year-old man was taken to hospital unconscious in Sera, in the western prefecture of Hiroshima, after collapsing near a river bank.
"He is suspected of having a heatstroke," a local ambulance worker told AFP by telephone.
More than 300 people were treated at hospital yesterday alone, the public broadcaster said as mercury rose past 30 degrees Celsius (86 Fahrenheit) in many towns across the nation.
The temperature reached 33 degrees C (91F) in central Tokyo by mid-afternoon today with over 36 degrees C (97 F) recorded in Tatebayashi, north of the capital.
