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.
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 garden mats or washing cars.
The heat wave that has recently swept across Europe is also gripping neighboring Slovakia. On Tuesday, a new national heat record of 41.3 was measured in the southern border region of Kamenica nad Hronom.
