The summer's first major heatwave has seen authorities in the countries along the Mediterranean's northern coast urging people to seek shelter and protect the most vulnerable.

"This is unprecedented," Agnes Pannier-Runacher, France's ecology transition minister said as a record 84 of the nation's 96 mainland departments were placed on the second-highest "orange" heat alert.

Ambulances stood ready near tourist hotspots as experts warned that such heatwaves, intensified by climate change, would become more frequent.

Firefighters were also on standby after blazes broke out Sunday in France, Turkey and Italy, fed by the heat and strong winds.

Cities are offering different ways of staying cool, from free swimming pools in Marseille to free guided tours for the elderly in air-conditioned museums in Venice.

- Records -

Temperatures in southern Spain soared to 46 degrees Celsius (115 degrees Fahrenheit) on Saturday, a new record for June, the national weather agency said on Monday.

"It's a bit difficult", said Agathe Lacombe, a tourist from Strasbourg visiting Madrid with her children and grandchildren.

"You have to adapt your whole day's planning, do everything in the morning and come home at the hottest times to find a bit of cool," she told AFP.

"We didn't anticipate it being so hot," said her daughter-in-law, Valentine Jung.

"It's a good thing we've got air-conditioning in our accommodation -- we didn't think of that when we booked!" she said.

A new record maximum temperature for June was also recorded in Mora in Portugal on Sunday, at 46.6 degrees, according to data from the national meteorological agency.

Seven regions in central and southern Portugal, including the capital Lisbon, were placed on red alert for the second day running Monday, with fire warnings in many forest areas.

In Italy, images posted by local media showed people running into the sea at a beach resort in Baia Domizia near Naples, as flames tore through pinewoods behind them.

"I have never experienced anything like this, we were surrounded by flames at least thirty meters high, smoke everywhere," the mayor of nearby Cellole, Guido di Leone, wrote on Facebook.

- Peak -

In France, the heatwave is due to peak on Tuesday and Wednesday.

No such luck for Italy, where the sizzling temperatures will continue to the end of the week and beyond, according to Antonio Spano, founder of the ilmeteo.it meterological website.

Authorities have issued red alerts for 18 cities across the country over the next few days, including Milan, Verona, Rome, Perugia and Palermo.

Scientists say climate change is stoking hotter and more intense heatwaves, particularly in cities where the so-called "urban heat island" effect amplifies temperatures among tightly packed buildings.

It has been particularly bad in Florence and Bologna, which have seen "incessant highs, every day for the whole week, certainly much higher than the norm", Spano told AFP.

The school year, which ends Friday in France, has already finished in Spain, Portugal and Italy, where some summer camps are subsidised as part of efforts to keep children cool.

- 'Not normal' -

In Croatia, the vast majority of the coastline was on red alert, while an extreme temperature alert was issued for Montenegro.

And with little relief in sight, the meteorological service in Serbia warned that "severe and extreme drought conditions prevail in a large part" of the country.

In Madrid, where temperatures approached 40C, 32-year-old photographer Diego Radames told AFPTV: "I feel that the heat we're experiencing is not normal for this time of year.

"As the years go by, I have the feeling that Madrid is getting hotter and hotter, especially in the city centre," he added.

With temperatures set to rise as high as 34 degrees, Britain's Met Office upped the number of amber heat alerts Monday to seven regions of England, where the Wimbledon tennis tournament was getting underway.

It is provisionally the hottest start to Wimbledon on record, with 29.7 degrees being recorded at the nearby Kew Gardens, the Met Office said.

"Wimbledon when it's really hot is quite sweaty. Last time we were very hot so this time we've got rose in a cooler so we can do a better job," Londoner Sean Tipper, 31, told AFP.

Tipper, visiting with his wife, mother and aunt, added that they'd also come prepared for the first day of matches with hats and sun glasses, plus "a mini fan and good hope".

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