Japan has endured its hottest summer since records began in 1898, the meteorological agency said Wednesday, during a heatwave that saw thousands of people taken to hospital suffering heatstroke.

The average temperature nationwide between June and August was 1.64 degrees Celsius above average for the period, forecasters said.

The previous record margin was 1.36 degrees C set in 1994.

The agency did not say what the average temperature was, but Tokyo's summertime temperatures averaged 27.1 degrees C (80.78 Fahrenheit).

In August, the mercury often soared above 35 degrees C in many areas of the country, the agency said.

"It can be said that weather was abnormal in this summer," an agency official, Shuhei Maeda, told a news conference. "The temperature is forecast to exceed 35 degrees centigrade in many places for a week to come."

Scorching summer weather led to at least 132 deaths and saw more than 30,000 people taken to hospital with heatstroke, the government said in mid-August.