The figures - just above the country's previous heat record from 2007 of 41.9 degrees - were recorded in the northern town of Szecseny, near the border with Slovakia.
The heatwave that has recently swept across Europe is also gripping the neighbouring country, where a national heat record was set on Monday with a temperature of 41 degrees.
Hungarian Prime Minister Péter Magyar has ordered work from home and shorter working hours in those professions where it is deemed possible. The government is also urging Hungarians to save water and, for example, to avoid watering border mats or washing cars.
