Tokyo, Aug 3 : The mercury across Japan skyrocketed with sweltering temperatures baking wide swathes from east to west, with temperatures hitting near-record highs of around 40 degrees Celsius in multiple areas. Such was the sudden rise in temperature on Tuesday, the Japan Meteorological Agency (JMA) issued a warning that people should take preventative measures to avoid succumbing to heat-related illnesses. People were also warned by a government alert, urging them to stay hydrated, refrain from making unnecessary trips or exercising outdoors and to use air conditioners to avoid heatstroke and heat exhaustion, Xinhua news agency reported. The weather agency said that temperatures were expected to soar to 41 degrees Celsius in Kumagaya, north of Tokyo, 39 degrees Celsius in Nagoya in central Japan and 37 degrees Celsius in central Tokyo. The JMA said a high pressure system over Japan started sending temperatures soaring on Tuesday. Meanwhile, as weather systems become unstable, Tohoku and Hokkaido regions in northern Japan are experiencing heavy downpours. This is owing to hot and humid air blowing into a low pressure system and the fronts in Japan's northern regions, public broadcaster NHK said. Due to high daytime temperatures and humid air, atmospheric conditions may become highly unstable in eastern Japan's Kanto-Koshin region later on Tuesday, said NHK, adding that some areas may be hit by thunderstorms, and downpours bringing more than 50 mm of hourly rain may occur. /IANS