A worker at a Tokyo Olympics construction site was found unconscious Thursday and was later confirmed dead at a hospital, the Tokyo Organizing Committee said, with police saying heatstroke may have been the cause.

Soaring temperatures have killed at least 57 people across the country since late July, highlighting the health threat to athletes and fans that is one of the biggest challenges for Olympics planners.

The 50-year-old construction worker who had been laying cables outside Tokyo Big Sight, which is being renovated to serve as the media center for Tokyo 2020, was found unconscious at around 2 p.m. on Thursday, the committee said.

“The cause of death is still unknown,” committee spokesman Masa Takaya said in an email, adding that they would provide more details once the cause of death was clear.

Working conditions for Olympic construction crews have come under scrutiny in the past.

In May, a report released by a global union federation demanded better conditions for laborers at Tokyo Games facilities after several “alarming” cases of suspected labor violations were uncovered.

The report from Building and Wood Workers’ International, titled “The Dark Side of the Tokyo 2020 Summer Olympics,” was based on interviews with construction workers and documented how low pay, overwork and poor access to grievance mechanisms were creating a “culture of fear” among crews working on Olympic projects.

Daytime temperatures in Tokyo have consistently stayed above 30 degrees Celsius since July 24, exactly a year before the games are set to open, with the heat intensifying in August to average daily highs of 34.8 C. It was 35.5 C in Tokyo on Thursday.

At least 57 people died across Japan in heat-related incidents between July 29 and Sunday and 18,347 were taken to hospital, according to the Fire and Disaster Management Agency. Tokyo had the most people taken to hospitals for heat-related medical issues nationwide, at 1,857, during the week.

Summer Olympics have traditionally been held during the northern hemisphere’s summer, but when Tokyo hosted the games in 1964 it was shifted to October to avoid the summer heat. The Mexico 1968 Olympics were also held later due to weather conditions.

Such shifts are no longer made due to international broadcasting rights holders and sports schedules, including the U.S. American football season and European soccer. The 2004 Athens Games and the 2008 Beijing Games were held in the summer despite concerns over the climate in both cities.

Olympics organizers plan to take steps to deal with the heat, including shaded rest areas, tents at security checkpoints, mist sprays and ice packs.

The start times for the women’s and men’s marathons, on Aug. 2 and 9, respectively, have been moved to 6 a.m. as an additional precaution.

Tokyo is hosting the Olympics for the second time, with the games running from July 24 to Aug. 9.