Both countries have seen above average temperatures for May.
ADVERTISEMENTHigh temperatures have been hitting France and Spain this week.
Large parts of Spain were under alert on Friday as a wave of intense heat began sweeping across the country.
Hot, dry air carrying dust from North Africa has pushed temperatures to 40°C in some Spanish regions, around 10-15°C above the average temperatures for May.
The State Meteorological Agency said it expected the “unusual and extreme” temperatures to peak on Saturday.
“These will probably be among the warmest temperatures we’ve seen in May in the 21st century,” agency spokesman Rubén del Campo said.
In the southern Spanish city of Jaén, the temperature climbed to 38.7 C (101.7 F) — 15 degrees above the seasonal average — in a record for the month of May.
The high temperatures are forecast to push northeast in the coming days, with little relief expected until after Sunday.
In France on Wednesday, May temperature records were equalled or broken in Albi (33.7°C), Toulouse (33.4°C) and Montélimar (33.8°C).
France's national meteorological service said it was "now very likely" that this month would become the hottest May on record.
"It is an episode of heat -- lasting, extensive and intense -- exceptional for the season," Matthieu Sorel, a climatologist at Météo-France, told AFP news agency.