The Foreign Office has issued an urgent warning for British holidaymakers jetting off to Spain.
It comes as the country's meteorological agency AEMET warned of an "extreme risk" of torrential rain and flash floods in Valencia, Alicante, Murcia and Almeria.
The area is expected to be hit on September 12 and 13.
The UK Foreign Office said flash floods could occur causing disruption and delays to transport services.
It said: "If you're in these areas, you should follow the advice of local authorities."
Weather service AVAMET said the region has seen its heaviest rainfall since records began in 1917.
In Valencia, fast-moving flood waters have reportedly already swept away vehicles.
The Mirror reported that a city street has been completely submerged after the Clariano River burst its banks.
More than 255,000 students have been told not to attend classes as schools have been closed as a precaution.
Weather forecasting company AccuWeather is predicting that downpours could measure 25-50 mm of rainfall through Friday, increasing the risk for flash flooding and mudslides.
AccuWeather meteorologist Eric Leister said: "Including what has already fallen, rainfall totals will average 75-150 mm in these areas."
Normal rainfall totals for the entire month of September range from 25-75 mm across eastern Spain.
