Red health alerts for extreme heat have been issued for more than half the country, with thermometers passing 46C (114.8F) on Saturday.
Parts of Portugal have already recorded temperatures of around 47C, while parts of Spain have reached 44C before the worst of the heatwave has even arrived. The record of Spain at 47.3 degrees Celsius was set in July previous year.
More than 700 firefighters are battling a major wildfire in southern Portugal, as temperatures in some areas approach record levels. That could push them above Europe's record high of 48C, set in Athens in 1977.
"In Britain, Friday could be as hot as last Friday, with 34C not out of the question".
A 41-year-old man suffered heatstroke while working on the highway close to Murcia, in southeastern Spain, on Wednesday.
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Temperatures are rising in Spain and Portugal aided by a wave of hot air coming from Africa.
On Thursday, temperatures reached 45.2C near Abrantes, Portugal.
British holiday-makers overseas are being warned to avoid spending time in the sun during the hottest part of the day and to keep hydrated.
On Friday, temperatures are likely to hit at least 29C and possibly 30C in southern parts of the United Kingdom, with temperatures elsewhere sitting at around 24C to 25C.
Sunday will be warm and dry in most places with sunny spells. Fires in Greece, Sweden, Finland, Norway, and Latvia have killed dozens of people and forced evacuations. Scientists monitoring the phenomenon say the glacier will lose its peak heading from the country to another location.
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UAE residents heading to Europe to escape the heat should be prepared for record summer temperatures sweeping the region which experts blame on global warming.
"The result of the hot summer will be a very big loss of snow and ice in the mountains", Professor of Geography Gunhild Ninis Rosqvist is quoted by the university as saying.
"Maximum temperatures will range from 16 to 22C in the north, and 20 to 32C in the south".
In the Middle East: Quriyat, Oman, likely set the world's hottest low temperature ever recorded on June 28, when the temperature failed to drop below 109°F, or 42.8°C.
The wide geographical spread of the heatwave, right across four continents, also points to global warming as the culprit..
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CNN's Laura Smith-Spark wrote and reported from London and Pau Mosquera reported from Madrid.