Europe sweltered under a multi-day heatwave that has triggered safety warnings. (Representational)

Belgian meteorologists registered record high temperatures on Thursday as western Europe sweltered under a multi-day heatwave that has disrupted transport and triggered safety warnings.

David Dehenauw, chief forecaster at the Royal Meteorological Institute, said a high of 40.6 degrees Celsius (105 Fahrenheit) had been recorded on the Kleine-Brogel military base, in northeastern Belgium.

"New Belgian national record: 40.6 in Kleine Brogel now and it's not finished yet! Unbelievable!" Dehenauw said on Twitter.

The temperature in Belgium exceeded 40 degrees for the second day in a row after it reached 40.2 degrees in Liege, the previous record, on Wednesday.

Thursday's new record is likely to be temporary as temperatures continued to rise in the middle of the afternoon.

In Brussels, the country's reference station, it was a record 38.8 degrees at 15:00 (1300 GMT), compared to 36.8 degrees an hour earlier in Europe's unofficial capital.

Since the beginning of official temperature records in 1833, it has never been so hot.

The previous record of 36.6 was set on in June, 1947.