In Germany, where temperatures set a new record again, people cooled off in lakes. (Photo: AFP)

Paris on Thursday baked in a record hot temperature of 41 degrees Celsius as a ferocious heatwave in northern Europe reached its peak, sparking concerns about public health and new misery for rail travellers.

As all-time temperature records tumbled in Belgium, the Netherlands and Germany in the last 24 hours, Paris saw its highest ever temperature of 41 degrees Celsius (105.8 Fahrenheit), beating the previous high of 40.4C (104.7F) set in July 1947.

Trains have been slowed in several European countries to avoid damage to the railway networks and French national operator SNCF has urged travellers to delay journeys planned for Thursday.

In the sweltering French capital, tourists and locals alike made a beeline for fountains and even pools laid on by the authorities next to the Ourcq canal in the north of the city.

Authorities have warned people to keep an eye on those living alone and also to beware of taking the plunge to cool down after a spike in drownings.

The scorching weather spelled misery for millions of commuters in public transport.

"Its so hot in the metro, it's unbearable. There are so many people, no air conditioning and everyone is on top of each other," said Paris commuter Petra Ulm, 34, a clinical researcher.

The heatwave, which is expected to ease up on Friday as rain and thunderstorms move in, had again focused public attention on the problems caused by climate change.

Train disruptions 

Hundreds of travellers were stuck on trains in sweltering conditions outside Paris for several hours late Wednesday after a fire on an electrical transformer halted traffic in and out of the Gare de l'Est station in Paris.

This came after a failure on an overhead power line had halted train traffic between Brussels and London and Paris. It was not immediately clear if the fault was due to the heatwave but Eurostar warned further disruptions were expected Thursday.

"I ask everyone who can avoid or delay their journeys to do so," said French Environment Minister Elisabeth Borne, saying workers who can do their jobs at home should not go to their offices.

"When it is this hot it is not just people in a fragile state who can have health problems," she warned.

In Austria, a three-year-old child died of dehydration after going to sleep in a car parked in full sunshine at the family farm, local authorities said.

'Look after people' 

Meanwhile, Britain's Met Office predicted a chance that the UK record of 38.5C, which was recorded in Faversham, Kent, in August 2004, would also be exceeded on Thursday.

The northern third of France, including Paris, was under a red alert while the rest of the country had a yellow warning and water-use restrictions were in force.

The Netherlands broke a record dating back to 1944 on Wednesday.

On Thursday, Germany again hit a national record of 40.9 Celsius (105.62F) in Lingen, West Germany.

Belgium on Thursday also reached a new record high of 40.6 degrees Celsius (105F), recorded on the Kleine-Brogel military base, in northeastern Belgium.

Paris, in particular, remains haunted by the early summer of 2003 when 15,000 deaths were blamed on the heat and the authorities were bitterly criticised for not mobilising fast enough.

"We need to take care of ourselves but above all others especially those who are alone, and be able to detect the first symptoms of heatstroke," said Prime Minister Edouard Philippe.

Local authorities have placed restrictions on water usage in many areas due to drought-like conditions that have seen ground and river water levels fall dramatically.

Climate change 

This summer's second heatwave has amplified concerns in Europe that human activity is heating the planet at a dangerous rate.

The June 26-28 blast of heat in France was four degrees Celsius (7.2 degrees Fahrenheit) hotter than an equally rare June heatwave would have been in 1900, the World Weather Attribution (WWA) team said this month.

One study by the Swiss Federal Institute of Technology said the deadly, weeks-long heatwave across northern Europe in 2018 would have been statistically impossible without climate change.