Paris/Madris: Hundreds of firefighters brought wildfires under control in southern France on Saturday as a stifling heatwave brought record-breaking temperatures to parts of Europe, killing at least six people.

In the worst-hit Gard region, where France's highest-ever temperature was registered on Friday at 45.9 degrees Celsius, scores of overnight fires burned some 550 hectares (about 1,360 acres) of land and destroyed several houses and vehicles.

"We came very close to a disaster," Didier Lauga, prefect of the Gard, told reporters. "There are still firefighters in place in case fires break out again."

A psychologically unstable man was arrested after starting a blaze in one village, but the extreme heat was likely to blame for many of the fires, Lauga said.

Fifteen firefighters and several police officers were injured in the Gard, where 700 firefighters and 10 aircraft were mobilised to contain the flames, emergency services said.

In the neighbouring Vaucluse region, authorities said a man who had been cycling in a mountainous area had died after collapsing due to the heat.

The sweltering conditions were expected to ease on Saturday in southern France but highs were still forecast at close to 40 degrees. Further north, Paris was due to experience its hottest day of the heatwave with a high of 37-38 degrees predicted.

As huge crowds took to the streets of the capital for the annual gay pride parade, firefighters sprayed water on revellers, some of whom used rainbow-coloured fans and umbrellas to counter the heat.

In Germany, organisers of Sunday's Frankfurt Ironman made contingency plans to keep athletes from overheating in temperatures expected to reach up to 38 degrees.

"Extreme risk”

The World Meteorological Organization said this week that 2019 was on track to be among the world's hottest years, and 2015-2019 would then be the hottest five-year period on record.

It said the European heatwave was "absolutely consistent" with extremes linked to the impact of greenhouse gas emissions.

Britain experienced its hottest day of the year so far with temperatures set to reach up 35 degrees, the Met Office said.

In Spain, unusually hot conditions were registered for a fourth consecutive day.

The mercury reached 43.3 degrees at a meteorological station between the Catalan towns of Vinebre and Masroig in northeastern Spain, close to an area hit by wildfires, officials said.

Forty of Spain's 50 regions have been placed on weather alert, with seven of them considered to be at extreme risk, the national meteorological agency said.

Two people died on Friday due to heat-related complications, and the sizzling temperatures fuelled several wildfires.

New blazes started on Saturday in southern and central areas, though firefighters managed to contain 90 per cent of the wildfires that raged across 60 sq km (23 sq miles) in the northeastern Tarragona province, the Catalan government said.

Two other fires in the central Castilla La Mancha and Madrid regions were still burning, affecting more than 30 sq km (11.5 sq miles) of land, officials said.

At least three people died in central and northern Italy, while hospitals in the financial capital Milan saw a 35 per cent rise in emergency visits due to heat-related conditions, local media reported.

Demand for power in the city surged as people cranked up air conditioning causing sporadic blackouts in stores and restaurants. Temperatures are forecast to ease in the coming days but it will remain hot.