Companies are reporting a drop in business, reflecting the economic toll of the heat wave, which is lowering productivity and keeping shoppers at bay.

Barcelona recorded its hottest month of June since records started over a century ago, Spain's national weather service said on Tuesday as Europe remained in the grip of the first major heat wave this summer.

Four people died in Spain, two in France and two in Italy as an early summer heatwave continued to grip much of Europe on Wednesday, triggering health alerts and forest fires and forcing the closure of a nuclear reactor at a Swiss power plant.