BSS/AFP) - Three lions from a Tokyo zoo have died from suspected heatstroke and others are under treatment, a spokeswoman said Tuesday, with the big cats struggling with high levels of humidity.

Japan sweltered through its hottest summer on record last year and parts of the country have hit 40C in recent weeks, qualifying for the new designation "cruelly hot day".

Since mid-July, 10 of the 16 lions in Tama Zoological Park have suffered symptoms such as "loss of appetite and decreased activity", and three lionesses died, the zoo said in a statement.

One passed away on Tuesday, another died on Friday, and the third died on Sunday, it said.

"According to our veterinarian, the cause of the deaths is suspected to be heatstroke" as dehydration and multiple organ failure were observed, a spokeswoman told AFP.

"Even though lions are thought to be resistant to heat, zoo keepers have been strengthening countermeasures to cope with Japan`s summer heat in recent years. Heat here comes with high humidity; that is different from heat with dry air in Africa," she said.

"But this summer, heat arrived suddenly after the rainy season was over" in late July, she said.

"We are strengthening measures against the heat (further), sprinkling water, improving ventilation and installing spot air conditioners," she said.

Several lions are still being treated, she added.

Close to 18,600 people were taken to hospital for heatstroke between July 20 and 26, with 45 of them pronounced dead on arrival, according to the fire and disaster management agency.

Japan experiences about 1,300 heat-related deaths annually and is aiming to halve that number by 2030.

Scientists say human-induced climate change is increasing the frequency and intensity of extreme heat events in Japan and elsewhere.

Its highest recorded temperature was registered on August 5, 2025, at 41.8C in Isesaki, north of Tokyo.

Authorities have adjusted the timings of a string of cultural and sporting events in recent years because of the heat, including the World Cosplay Summit in Nagoya, which held its last summer edition last weekend.