Meteorologists have placed more than half of France, including around Paris, on alert for high temperatures as a heatwave was expected to spread across Europe.
National weather agency Meteo France predicted the hot weather could produce temperatures of up to 40C (104F) across the country just as the summer tourist season shifts into high gear.
The French weather agency set the heat warning level at orange - the second highest intensity on its four-level categorisation system for potentially dangerous conditions requiring public vigilance.
In Paris, charity organisations patrolled the streets to provide homeless people with water, while local authorities organised air-conditioned public places where people could seek shelter from the heat.
French education minister Jean-Michel Blanquer, deciding it was too hot to study, ordered national exams taken by students heading to high school to be postponed from Thursday and Friday to next week.
International football federation Fifa could face implementing heat precautions at the Women's World Cup, which France is hosting. The precautions include holding cooling breaks during matches and postponing games if the heat is too intense.
Women's World Cup matches are scheduled every day this week, except Wednesday and Sunday. Luckily, most were set to be played at night.
France introduced a heat watch warning system after a long, deadly heatwave in August 2003.
The highest temperatures in more than half a century eventually were estimated to have caused 15,000 heat-related deaths, many of older people left in city apartments and retirement homes without air conditioning.
French President Emmanuel Macron said that vigilance was the watchword for the week.
"As you know, at times like these, sick people, pregnant women, infants and elderly people are the most vulnerable. So we must be vigilant with them and have prevention measures in place in order to intervene as quickly as possible," Mr Macron said.
French health minister Agnes Buzyn said that "everything is ready" in retirement homes, hospitals and transportation systems.
"Yet when people are fragile, even when everything is organised, there's always a higher mortality rate," she warned.
Meteorologists said hot winds from the Sahara Desert brought the scorching weather to Europe. Similar heat is expected in Belgium, Switzerland and Germany.
In Germany, temperatures above 40C are possible in some places on Wednesday, topping the country's previous June record of 38.2C, set in Frankfurt in 1947.
Parts of north-eastern Germany are also at high risk for forest fires. Authorities in the eastern state of Brandenburg, which circles Berlin, said the risk of forest fires is at the highest level in the coming days.
Scientists say measurements show that heatwaves in Europe are becoming more frequent.
Stefan Rahmstorf, of the Potsdam Institute for Climate Impact Research, said "monthly heat records all over the globe occur five times as often today as they would in a stable climate".