The Foreign Office has extended an alert over extreme temperatures in Italy to include both Greece and Spain.
The travel advice was updated as wildfires broke out near Athens due to the heatwave spreading across many Mediterranean countries.
A group of 1,200 children were reported to have been evacuated as flames approached their summer camp in the coastal town of Loutraki, west of Athens.
However, Advantage Travel Partnership chief executive Julia Lo Bue-Said indicated that UK holidaymakers were not being put off.
In a tweet, she said: “As the Met Office forecast a month of rain in the UK, is the heatwave across Europe slowing down demand for travel this summer. Nope. The opposite.”
The latest official travel advice for Greece and Spain highlights “extreme temperatures”.
In Greece this could cause travel disruption over the extended summer period, according to the Foreign, Commonwealth & Development Office (FCDO).
It recommended UK travellers to visit the NHS website for information on how to take care in the heat.
Those heading to Greece should also monitor local weather updates and register with the country’s emergency communication service to receive alerts.
The travel advice for Spain said: “You should check with your travel provider before travelling and follow the advice of local authorities at all times.”
The Spanish state meteorological service AEMET warned of temperatures of between 42C and 44C and issued top-level red alerts for some interior parts of the country and the Balearic Islands.
Italy’s national meteorological service also issued red alerts for extreme heat in southern Italy, Sicily and Sardinia, with temperatures well above 40C. Parts of the Balkans are also under red alert.
The heat is forecast to intensify by the middle of the week in parts of the Mediterranean, including Greece and Turkey, according to the UN World Meteorological Organisation (WMO).
Greece has hit temperatures of 40C or more in recent days. The Acropolis in Athens – the country’s most popular tourist attraction – was closed during the hottest hours of Friday and Saturday to protect visitors.
Regular opening hours were resumed on Monday but a new heatwave is expected later this week.
Meanwhile, parts of Asia have been affected by storms and heatwaves and 80 million in the southern states of the US are under advisories as a “widespread and oppressive” heatwave hit the region, according to the BBC.
WMO secretary general Petteri Taalas said: “The extreme weather – an increasingly frequent occurrence in our warming climate – is having a major impact on human health, ecosystems, economies, agriculture, energy and water supplies.
“This underlines the increasing urgency of cutting greenhouse gas emissions as quickly and as deeply as possible.
“In addition, we have to step up efforts to help society adapt to what is unfortunately becoming the new normal.
“The WMO community is providing forecasts and warnings to protect lives and livelihoods as we strive to achieve our goal of early warnings for all.”