The heatwave, with temperatures reaching as high as 40°C, is expected to continue.
Paris temperatures reached 39.7°C on Wednesday.
This is the hottest that it has been in the capital since 1947.
Delays hit train services in the Ilde de France region around Paris on Wednesday.
On Thursday rail company boss Guillaume Pepy blamed the inability of the power supply wires to cope with the high temperatures.
"When it's 40°C we must take even more precautions because safety comes first," he told BFM TV. "There will be delays."
Pepy also said trains are running slowly because it is peak tourist season, estimating that about 24 million tourists use the network during vacation season from July to August.
The heatwave has not only caused travel delays it has also caused power outages in parts of France.
Pollution levels have also increased.
At the beginning of the heatwave the levels were orange but Friday and Saturday they will be classifed as red, a higher level of pollution.
The heatwave has also affected Portugal, Spain, Britian, nothern Italy, Belgium and the Netherlands.
Authorities are warning everyone to drink water and try to stay in the shade.