Sweltering temperatures across Japan have left at least three people dead and 3,000 others taken to hospital with heatstroke in the course of a week, officials said Wednesday.

The state weather agency said temperatures topped 35 degrees Celsius (95 degrees Fahrenheit) in several places Wednesday, warning that similarly hot weather would "raise the danger of heatstroke" the next day.

The Fire and Disaster Management Agency said three people died from heatstroke last week while a total of 3,179 people were taken to hospital, rising from 2,473 a week earlier.

The mercury soared past 30 degrees Celsius last week with high humidity as the country's month-long rainy season was coming to an end.

Among the dead was a 76-year-old woman who collapsed inside a greenhouse, public broadcaster NHK reported.

Nearly half those needing hospital treatment were aged over 65.