The French health minister says only about 4 percent of visits to hospital emergency rooms across the country are linked to the current heatwave, which the government considers a relatively low level.

Agnes Buzyn, visiting the Necker pediatric hospital in Paris on Sunday, said 18 out of 650 emergency services in France were considered "under tension" due to more patients and a lack of staff, especially in the northeast, where this week's high temperatures are more unusual.

Buzyn warned against carrying small babies in wrap carriers - which tends to keep them warm - and to watch out so that children under six don't drown in private swimming pools.

The heatwave in France is expected to last until Thursday, with temperatures peaking on Tuesday.

Four nuclear reactors have already been temporarily closed in France due to the high heat.