Forty people have drowned across France as a sustained extreme heatwave tightened its grip on Europe Monday, with governments from London to Rome escalating emergency responses and body counts rising.

French authorities confirmed the drowning deaths — most linked to rivers and lakes as residents sought relief from temperatures that have pushed night-time lows above 30C in parts of Spain. France convened a government crisis meeting to coordinate the national response.

Italy's health ministry declared a red alert across major cities, the highest level in its heat-warning system, advising the elderly and vulnerable to remain indoors during peak afternoon hours.

In the United Kingdom, the Met Office issued red temperature warnings after forecasters said readings could reach 39C — close to the country's all-time record of 40.3C set in July 2022. Millions of workers and commuters faced disruption as rail operators warned of speed restrictions on heat-warped tracks.

Across the continent, emergency services reported surging demand for heat-related medical calls. Hospitals in southern France and northern Italy reported elevated admissions for heatstroke and dehydration.

The heatwave is forecast to persist across western and southern Europe through at least Wednesday, when a break in pressure is expected to bring limited relief to northern France and the Low Countries. UK temperatures are expected to peak Tuesday.