Belgium officially registered its first-ever September heatwave on Friday, as temperatures in Brussels topped 25 degrees Celsius (77 Fahrenheit) for a fifth straight day, the country's meteorological agency said.

"We are currently experiencing the 48th heatwave since records began in 1892, but above all the very first heat wave recorded in the month of September," Belgium's Royal Meteorological Institute said.

The institute said temperatures at a monitoring station in the south of the capital hit 26.1C on Monday before rising above 30 degrees since Tuesday.

The temperature on Friday was registered at 30.3C in the shade.

Belgium officially designates a heatwave if the temperature rises above 25C for at least five consecutive days, with temperatures going over 30 on three of those days.

The heatwave in the country is expected to last through Monday.

Prolonged episodes of higher temperatures are becoming more frequent in June, July and August in Belgium, a country traditionally known for its gloomy weather.

Nearby Britain is also experiencing a record-breaking heatwave that has prompted an amber health warning from authorities.

2023 is likely to be the hottest year in human history, and global temperatures during the Northern Hemisphere summer were the warmest on record, the European Union's climate monitor said this month.

UN Secretary General Antonio Guterres warned that the global "climate breakdown has begun" and the global body has said much more needs to be done to address the crisis.