The zoo said that 10 of its 16 lions have been ill. Japan has been experiencing an extreme heatwave since late July.

Japan sweltered through its hottest summer on record last year and parts of the country have hit 40 degrees in recent weeks.

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

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 Tokyo zoo said in a statement.