TOKYO, May 27 (Xinhua) -- A heatwave continued to score wide swathes of Japan Monday, with the weather agency warning that unseasonably high temperatures were set to continue.

According to the Japan Meteorological Agency (JMA), the mercury surged above 30 degrees Celsius in many parts of the country, with 340 out of 926 monitoring posts registering temperatures above 30 degrees C.

The mercury was above 30 degrees C for a fourth straight day in Japan's capital city of Tokyo, marking a new record for the month of May, the JMA said, while in Obihiro in the northernmost prefecture of Hokkaido, temperatures hit 35.5 degrees C.

The mercury rose to a record 39.5 degrees C on Sunday in the town of Saroma in Hokkaido, with scorching temperatures through Monday forcing more than 50 local train services in Hokkaido to be canceled due to the risk of tracks buckling under the heat.

Over the weekend more than 100 people were admitted to hospitals in Tokyo alone suffering from heatstroke, the Tokyo Fire Department said, with the figure for heatstroke casualties already topping last year's figure of 142 for May, at 237 for the month so far.

Officials from the fire department have warned people to stay hydrated and to avoid spending prolonged periods in direct sunlight.

They have also urged people to keep their rooms well ventilated and to take other measures to prevent against heatstroke and other heat-related illnesses.