A new heat record of 40 C for the day was measured in Fülöpháza, in central Hungary, on Thursday, the national weather service (OMSZ) reported.
According to OMSZ, such high temperatures have not been measured in June since 1901, when the institute started its observations.
Nationwide, the highest average temperature reached 37 C, about 10 C higher than usual.
The Budapest record has also been broken, with 38.1 C in northern parts of the city, compared to the previous record for the day, 35.2 C, measured in 2002.
The previous heat record for the country was also measured in 2002, at 38.4 C, in Bekescsaba, in south-eastern Hungary.