PARIS, July 24 (Xinhua) -- The national weather center, Meteo France on Wednesday placed twenty departments in northern France, including Paris and surrounding communes on heatwave red alert -- the highest level on the agency's four scale, and urges residents to be extremely vigilant.

The warning will be maintained till Friday morning as mercury is set to climb in the concerned zones, with records of maximum temperatures could be beaten, the agency predicted.

It added that 60 regions remained on orange alert as hot spell is still engulfing 90 percent of French territory.

"Following this unprecedented alert in France, everyone must feel concerned and redouble vigilance towards the most fragile and towards oneself, even when one is healthy," health minister Agnes Buzyn said.

On Wednesday afternoon, temperatures swing between 31 and 36 degrees Celsius in western areas and between 36 and 41 degrees Celsius notably in southeastern, northern France, according to Meteo France.

"Thursday will be the hottest day ... with expected maximum temperatures above 40 degrees, notably over the country's northeastern areas," it forecasted.

People are recommended to stay indoors, keep cool and drink at least 1.5 liters of water a day to prevent heatstroke.

Authorities have activated a level-three heatwave action plan which involves setting up "cool rooms" in municipal buildings, opening pools for late-night swimming and offering access to garden parks by nightfall to help people cool off.

At the end of June, an unseasonably hot weather brought record-breaking temperatures to most French regions.

In the southern city of Gallargues-le-Montueux, temperatures reached 46 degrees Celsius -- the highest on record. It was nearly two degrees above the previous high of 44.1 degrees recorded in August 2003.

France, where temperature average stands at 19.9 degrees for the June-August period, is witnessing "more intense and more frequent heatwaves " due to climate change, warned Meteo France.