Three lionesses at a Tokyo zoo have died from suspected heatstroke after an intense spell of hot and humid weather swept across Japan, while several other lions remain under veterinary care.

According to The Guardian, 10 of the 16 lions at Tama Zoological Park have shown signs of illness since mid-July, including loss of appetite and reduced activity. The zoo confirmed that the three lionesses died on Friday, Sunday and Tuesday.

Veterinarians suspect heatstroke as the cause of death after observing severe dehydration and multiple organ failure in the animals.

Zoo officials said that although lions are generally considered tolerant of high temperatures, Japan’s humid summer conditions pose a different challenge from the dry heat of their natural African habitats.

“The heat here comes with high humidity; that is different from heat with dry air in Africa,” a zoo spokesperson said, adding that temperatures rose sharply after the rainy season ended in late July.

The zoo has stepped up measures to protect the remaining lions, including sprinkling water around enclosures, improving ventilation and installing spot air conditioners. Several lions are still receiving treatment.

Japan is experiencing another exceptionally hot summer after recording its hottest summer on record last year. Parts of the country have recently exceeded 40°C, meeting the government’s newly introduced “cruelly hot day” classification.

The Guardian reports that between 20 and 26 July, around 18,600 people were hospitalised with heatstroke across Japan, while 45 people were declared dead on arrival, according to the country’s Fire and Disaster Management Agency.

The extreme temperatures have also forced organisers to adjust the schedules of major cultural and sporting events. Scientists say human-induced climate change is making extreme heat events more frequent and intense in Japan and other parts of the world. South Korea is also experiencing a severe heatwave, with rising summer temperatures linked to at least 16 deaths.