Zero-degree line at record height above Switzerland as heat and fire hit Europe

Weather ballon climbs to 5,300 metres before temperature falls to 0C amid late summer heatwave

A Swiss weather balloon had to climb to an unprecedented 5,300 metres (17,400ft) before the temperature fell to 0C (32F), meteorologists have said, as a late summer heatwave and wildfires continue to pummel swathes of continental Europe.

A man was found dead in a blaze raging north of Athens on Monday as the Greek government warned of an extreme" risk of fire across the country, while more than half of mainland France was placed under an amber heat alert.