Three lionesses have died from suspected heatstroke at Tama Zoological Park in Tokyo, as the animals struggle with high levels of humidity.
Since mid-July, 10 of the zoo's 16 lions have suffered symptoms such as loss of appetite and decreased activity. A spokesperson said on Tuesday that other lions are currently undergoing treatment.
The illness coincides with an extreme heat wave in Japan. Parts of the country have hit 40C in recent weeks, qualifying for the new "cruelly hot day" designation, after the country sweltered through its hottest summer on record last year.