Two people have been killed and hundreds treated in hospital after a weekend heatwave swept over Japan, officials and reports said Sunday.

A 74-year-old women collapsed while working in a greenhouse in the eastern prefecture of Chiba on Saturday 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.

On Sunday, 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.

The official said there were unconfirmed reports that the man had been working in rice paddies before collapsing.

More than 300 people were treated at hospital on Saturday 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 Sunday with over 36 degrees C (97 F) recorded in Tatebayashi, north of the capital.