Three lions at a Tokyo zoo have died from suspected heatstroke and others are under treatment, a spokeswoman said on Tuesday, with the big cats struggling with high humidity. Ten of the 16 lions in Tama Zoological Park have suffered symptoms such as "loss of appetite and decreased activity" since mid-July, and three lionesses died, the zoo said in a statement. The Tama Zoological Park said the lion enclosure, where visitors can normally be driven around in zebra-pattern "safari" buses, was closed to the public until further notice. "According to our veterinarian, the cause of the deaths is suspected to be heatstroke" because 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.