Severe weather warnings have been issued for European destinations popular with Irish holidaymakers due to scorching conditions.
Temperatures are forecast to exceed 40C (104F) as a heatwave sweeps across the south of the continent.
Meteoalarm, which is a network of national meteorological services in Europe, issued alerts for "very dangerous" weather due high temperatures in 11 countries such as Italy, Switzerland, Poland and Croatia.
It urged people to "follow orders and any advice given by your authorities", adding that "extraordinary measures" could be introduced.
Temperatures are expected to reach 41C (106F) in Seville, Spain; 39C (102F) in Rome, Italy and 38C (100F) in Athens, Greece.
A spokeswoman for the travel trade organisation Abta said with very high temperatures being recorded across Europe, holidaymakers are being advised to make sure they take sensible precautions to avoid sunstroke and other serious problems that can result from over-exposure to heat and powerful sunshine.
"Holidaymakers should ensure they stay hydrated by drinking plenty of bottled water, particularly the young or elderly.
"Abta would also advise that British travellers follow the lead of the locals in their destination by staying out of the sun at the middle of the day when it is at its peak, and follow any advice issued by health authorities in specific destinations."
Italian authorities told people in affected regions to "only travel if your journey is essential", while Polish officials said: "Protect yourself and support vulnerable people. Expect possible infrastructural breakdowns."
Tourists were among 10,000 people evacuated after forest fires in the French Riviera last week.
Tourists also had to be rescued from the Italian island of Sicily because of wildfires.
The Foreign and Commonwealth Office advised visitors to Italy that forest fires are "dangerous and unpredictable", adding that the risk of further blazes will remain throughout the summer.
Conditions are considerably cooler for those staying in Ireland. It will be partly cloudy in the morning with showers spreading eastwards across Ireland. The afternoon will then have a mixture of sunny spells and areas of cloud with further showers in places, these perhaps locally heavy and prolonged over Ulster and Connacht. A gentle to moderate westerly breeze with maximum temperatures of between 14 and 18.