Spain also issued warnings of extreme heat for its southern areas, with temperatures expected to reach 45 C (113 F) in the cities of Seville, Huelva, Badajoz and Cordoba.
The current European record of about 118 degrees Fahrenheit (48 degrees Celsius), which was registered in Athens during the summer of 1977, could be broken in the Iberian Peninsula, which includes Spain and Portugal, said Becky Mitchell, a meteorologist with the national weather service in the United Kingdom (U.K.).
The big picture: The heat wave will be most intense in Portugal, Spain and parts of France, although the United Kingdom will also see above average temperatures for this time of year.
Europe's weather warning group, Meteoalarm, has already issued red warnings - categorised as very risky and posing a risk to life - for much of southern Portugal and for the Badajoz province in Spain.
Holidaymakers heading to Spain and Portugal were warned of an extreme heatwave which could see the hottest temperatures ever recorded in continental Europe.
Collecting data about the weather and the number of deaths from 1984 to 2015 in the Americas, Asia and Africa, as well as using a mathematical model, a team of scientists from Monash University in Melbourne assessed the estimated level of death from high temperatures in the period from 2031 2080 for the year.
Eight places in the centre, south and east of Portugal broke their local temperature records, with officials forecasting on Friday the heatwave would continue and possibly worsen over the weekend.
Temperatures could reach 48C in Spain and Portugal today.
They are set to build across Portugal on Friday and Saturday, with medical staff and firefighters on standby until the end of the weekend.
"Oh it's bad", said tourist Paul Snell. Two died of heatstroke in the southeastern region of Murcia, Spanish radio Cadena Ser reported, while another man died in Barcelona on Friday, emergency services said.
Although nowhere near the roasting conditions in southern Europe, the Met Office is still urging people to stay "sun sensible" - drink lots of water and stay out of the sun in the hottest part of the day.
Love Island might be over, but it looks like we're still in for a long, hot summer.
In Scandinavia, temperatures hit records until a few days ago.
June's average United Kingdom maximum temperature was 19.9C, the same as June 1976.
Authorities on both sides of the Baltic Sea, in Sweden and Poland, have advised against swimming due to a huge bloom of heat-fuelled toxic algae.
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