After heavy rain soaked the Opening Ceremony on Friday and Saturday, the Paris Olympics were faced with very different conditions on Tuesday, with temperatures reaching 36 degrees Celsius and rain overnight on Tuesday and early Wednesday morning.

To make matters worse, the French meteorological service issued a severe weather warning for the capital, warning of thunderstorms, heavy rain, hail and lightning in the afternoon.

While the rain on Tuesday night and early Wednesday morning brought some relief to athletes, spectators and officials, temperatures began to rise again throughout Wednesday.

Temperatures reached 32 degrees, which can affect the performance of athletes and the general public, who flocked to various Parisian water sources to cool off.

Paris has been hit by a series of record-breaking heatwaves in recent years, with temperatures topping 42 degrees in 2019.

A report released last month ahead of the Games, backed by climate scientists and athletes, warned of the dangers of extremely high temperatures.

At Roland Garros, where Rafael Nadal and Carlos Alcaraz were competing in the men's doubles, stadium announcers urged tennis fans to take breaks from the scorching heat in cooler areas of the grounds.

Britain's Jack Draper described the conditions as "brutal". Players were provided with refillable water bottles, but the world number 27 said it was impossible to keep the water cool.

"We were drinking hot water out there," said Draper after his exit to Taylor Fritz of the United States. "It's no fun in those conditions."

Tennis officials activated a heat protocol, allowing a 10-minute break between the second and third sets.

It was a similar situation on the final day of the football group stage, with two extra breaks for players to cool off on top of the mandatory 15-minute half-time break.

The stark contrast to Friday's opening ceremony, when it rained heavily and was considerably cooler, was not lost on German hockey player Christopher Ruehr.

"It was a big change from the last few days when it was raining and 20 degrees, but we all have to deal with it," said Ruehr after scoring in the win over South Africa.

"We have ice vests, which are just cool vests that we put over our jerseys to cool down a bit, and we have ice towels," said Ruehr.

British rider Carl Hester said it was vital to keep his horses cool during the competition at the sun-drenched Château de Versailles, the former royal residence some 19 kilometres west of Paris.

It was no less tough for spectators at outdoor events, even though some venues had lamppost-like devices that sprayed water on spectators like a light shower.

In a fan zone in the heart of the capital, at the Hotel de Ville, visitors enjoying the action on big screens fanned themselves with whatever they had at hand and were helped to cool off by light sprays of water.

When asked if it was too hot to enjoy the sporting drama unfolding on the screens, Brazilian tourist Enzo Calgano, 30, said, "At the end of the day, the Olympics are more important than the heat."

Those who get no respite from the heat are the various security forces, who seek any natural shade or under trees to escape the punishing sun, especially considering they are not in summer uniforms and some wear special vests.

The weather forecast for the coming days is unstable, with high temperatures intertwined with possible precipitation that could lower the temperatures in a Paris with few people on the streets.