After days of record-breaking temperatures around Europe, officials have warned people to adjust their behaviour – even fit, young people – as health services report a sharp rise in life‑threatening emergencies.

In London, the ambulance service faced its busiest day on record this week, with cardiac arrests up nearly a third, and is urging people to drink responsibly and avoid exercise outside.

Parisians, meanwhile, will be restricted from drinking alcohol in public from noon through the night on both Friday and Saturday.

Extreme heat puts immense physical strain on the body – made worse if you are dehydrated from drinking alcohol – with the heart pumping harder and faster to cool you off.

In the UK, ahead of England playing Panama in the World Cup on Saturday, people are being advised to drink plenty of fluids but not lots of alcohol in this punishing heat, to avoid dehydration.

Alcohol is a diuretic, which means it makes you pee more, while the hot weather also makes us sweat lots.

“This dehydration double whammy makes it even more important to drink plenty of water and stay as hydrated as possible throughout the day,” says Alcohol Change UK.

During the heatwave, the nights have been hot too, presenting its own challenge. It means the body cannot cool down as much in between the daytime heat spikes.

Heat exhaustion can affect anyone, including fit and healthy people – especially if they have done strenuous exercise in high temperatures or been drinking alcohol in the sun all day. It can come on quickly, over minutes, or gradually, over hours.

It can subsequently turn into heatstroke, external, which is a medical emergency. It means your body can no longer manage the heat and your core temperature is rising too high. There can be fast breathing or shortness of breath and collapse or unconsciousness. Get urgent medical help.

People are being reminded that it’s fine to take a couple of days off from exercising, given the hot weather. If you are going do something physical outdoors, dial it down, pace yourself and stick to times of the day when it is cooler, such as the very early morning or late evening, experts advise.

Paris mayor Emmanuel Grégoire told French TV people must not believe they are “invulnerable”.

“I am thinking especially about the youth…I saw 100 or so joggers on the street. Frankly, that’s irresponsible.”

The London Ambulance Service says it responded to its highest number of life-threatening emergencies ever on Wednesday when the UK’s capital had temperatures in the mid-30s.

It saw a 50% increase in life-threatening emergency calls compared with a typical Wednesday in June, with the number of cardiac arrests up 30%.

Chief operating officer Craig Harman is advising people to drink plenty of water in between alcoholic beverages, as football fans prepare to cheer on England on Saturday, when temperatures are still expected to exceed 30C.

“I’m saying to people I need you to drink water even when you’re not thirsty, staying out of the sun during the hottest parts of the day, and particularly not exercising outside and putting your body under additional heat and strain,” he said.

France’s Health Minister Stéphanie Rist warned “young people are also suffering from cardiac arrests”.

The ambulance service in Paris had seen four times more cardiac arrests than normal over a 24-hour period, although there are no confirmed figures for the number of deaths linked to the heatwave yet.