Spain's weather agency, Aemet, has issued red warnings for heat in parts of the southwestern Extremadura and Andalucia regions Saturday, while swathes of the rest of the country are under orange or yellow alerts for heat.
Hot air from North Africa has caused the most severe heatwave in Iberia since 2003, one of the worst years on record for forest fires.
Friday saw local all-time record temperatures at nearly half the country's weather stations.
If the weather forecast is confirmed, it would be the most significant heatwave in Europe in the last 41 years.
The World Meteorological Organisation said Europe's record is 48C in Athens, Greece in 1977.
The country's civil protection agency reported 426 firefighters were putting out fires or checking alerts in the north and centre of the country.
Fires typically flare late in the day when the weather is hottest.More news: Apple becomes the world’s first trillion-dollar company
Temperatures were forecast to reach 44 degrees (111 Fahrenheit) Thursday in the Portuguese city of Evora, 130 kilometers (81 miles) east of the capital of Lisbon, and in the Spanish province of Badajoz, across the border.
In Greece high winds fanned unsafe wildfires which killed more than 90 people.
"Even if they don't reach the 48 [degrees Celsius], they could break their own individual records as a country as well", she said.
According to him, temperatures in the Iberian peninsula may be higher than those recorded in the last 40 years.
People cool off in an urban beach at Madrid Rio park in Madrid, Friday, Aug. 3, 2018.
In Spain, heat stroke killed at least three men. Fishery authorities in the canton of Zurich were combing creeks to rescue fish from suffocation as streams dry up or oxygen levels plunge.
BBC weather meteorologist Nick Miller says the recent wave may hit record highs and is "potentially unsafe".
July's average United Kingdom maximum temperature was 22.6C from July 1-30, hotter than 1976's 21.6C, and the second-hottest since records began 108 years ago in 1910, behind only 2006's 23.2C.
Meanwhile, authorities on both sides of the Baltic Sea, in Sweden and Poland, have warned against swimming due to a huge bloom of toxic algae spreading because of hot temperatures.