A single flash of lightning in the United States nearly two years ago cut across the sky for nearly 770 kilometres, setting a new world record, the United Nations said yesterday.

The new record for the longest detected megaflash, measured in the southern US on April 29, 2020, stretched a full 768 kilometres, or 477.2 miles, across Mississippi, Louisiana and Texas.

That is equivalent to the distance between New York City and Columbus, Ohio, or between London and the German city of Hamburg, the UN's World Meteorological Organization (WMO) pointed out in a statement.

That lightning bolt zig-zagged some 60 kilometres further than the previous record, set in southern Brazil on October 31, 2018.

The WMO's committee of experts on weather and climate extremes also reported a new world record for the duration of a lightning flash.