Third-degree heat alerts are issued when the median temperature reaches 27 degrees Celsius for three days in a row.
Daytime highs are forecast to reach 40 degrees in the second half of the week, with lows not falling below 20 degrees in certain places.
Young children, the elderly and those with cardiovascular diseases should take particular precautions, the statement said.
The heat alert comes with advice to drink plenty, avoid the sun between 11am and 3pm and to use skin protection.
Gergely Karacsony, the mayor of Budapest, said in the afternoon that he has asked public companies to take concrete measures in the capital. Budapest Public Transport Centre (BKK) will distribute drinking water at busy traffic spots including downtown Deak Square, the Keleti Railway Station and Szell Kalman Square. The Budapest Water Works has also put out into the street a vehicle equipped with a tank providing drinking water to pedestrians. Budapest’s public infrastructure maintenance company will keep sprinkling water onto roads and baths in the city will operate with extended opening hours, Karacsony said