The heat and humidity in Japan have become a major hurdle for athletes competing at the Tokyo Olympics, even though organizers stress they have taken sufficient steps to prevent such conditions from posing a health hazard to them.

With endurance events like marathons and race walking coming up in the northern city of Sapporo, where the temperature recently reached 35 C for the first time since 2000, concerns have mounted over the impact of the scorching heat on the athletes' performance and health.

Athletes compete in the first round of the women's 3,000-meter steeplechase at the Tokyo Olympics on Aug. 1, 2021, with heat haze seen over the track of the National Stadium amid scorching summer heat in the capital. (Kyodo) ==Kyodo

Since the Olympics started July 23, the extreme heat in the capital, with the mercury climbing as high as 34 C on some days, has already taken a toll on athletes during what may be the biggest competition of their lives.

The starting times of tennis matches were pushed back later in the afternoon after players, including world No. 1 Novak Djokovic and No. 2 Daniil Medvedev, complained of the dangers of playing under the midday sun. A Russian archer had reportedly collapsed due to the heat during qualifications.

Triathletes were photographed collapsing on the ground after the men's event on July 26, and gold medalist Kristian Blummenfelt of Norway said he worked extensively to get used to Japan's climate during training.

Across the country, 8,122 people were taken to the hospital between July 19 and July 25 due to heat-related incidents, nearly double the number of cases reported the previous week, according to the Fire and Disaster Management Agency.

As part of the heat countermeasures, the Olympic organizers have prepared water bottles to keep athletes hydrated, with mist fans and ice baths installed at some competitions. They also said that the athletes' lounge will be air-conditioned.

During the tennis tournament, Medvedev told reporters that he was "just ready to fall down on the court" before the International Tennis Federation announced that the start time of matches was moved from 11 a.m. to 3 p.m., five days after the opening ceremony of the Olympics.

Daniil Medvedev of the Russian Olympic Committee wipes sweat away as he struggles with the extreme heat during a Tokyo Olympic men's singles third round match against Italy's Fabio Fognini at Ariake Tennis Park in the capital on July 28, 2021. (Kyodo) ==Kyodo

"I couldn't breathe properly," he said. "I had darkness in my eyes like between every point. I didn't know what to do to feel better. Like, I was bending over, but I couldn't get my breath together."

One female volunteer assigned to the Ariake Tennis Park said she thought it was "disrespectful" to have top athletes play under these punishing conditions.

"If they need to play under such heat and humidity, I think none of the athletes will think about playing in Tokyo in the future. I think it is very rude," she said.

The volunteer said she did not feel her volunteer work to be so physically challenging because her shift had been a rotation of working indoors and outdoors, and she was given drinks and cooling pads by the organizers.

The organizing committee has reported about 30 cases of heat-related sickness among Olympic personnel, most of them among volunteers and contract workers, but it maintains that it is doing well so far.

"We believe heat measures are extremely important for us," Toshiro Muto, CEO of the organizing committee, told a press conference on Sunday. "It is something we need to continue looking into."

"Before the coronavirus became a problem, drawing up heat countermeasures for the Tokyo Games was our biggest challenge. At the time, we considered (the measures) by looking into different scenarios to prepare thoroughly," he said.

"I think our response has been working so far."

With the games held mostly behind closed doors due to the coronavirus pandemic, the organizers do not have to worry about the millions of people initially set to go to venues to watch events, some of which can last a few hours.

The committee launched a weather information center last month to provide venue-to-venue condition data, such as temperature, humidity and wind conditions, with support from the Japan Meteorological Agency.

"I think it's difficult for athletes to compete, especially if they are not from Japan. The safety and the health of athletes should be the top priority," said Shinobu Hiroki, an Olympic fan in Japan.

"The organizers could have predicted that the temperature will be this high. I wonder if the current situation could have been prevented," she said.

When Tokyo was bidding for the 2020 Olympics eight years ago, it said in its candidature file, "With many days of mild and sunny weather, this period provides an ideal climate for athletes to perform at their best."

Marathons and race walking, arguably the most physically punishing competitions left on the Olympic schedule, were moved to Sapporo in the country's northernmost main island of Hokkaido in 2019 to escape the capital's deadly summer heat.

But the weather agency predicts that the mercury might hit as high as 34 C on the weekend when the women's and men's marathons will be held.