Sydney Zoo's "beloved" chimpanzee Mogli has died unexpectedly.
In a Facebook post, the zoo said the primate was found dead in its enclosure at the Blacktown site on Friday morning.
"We are currently investigating the circumstances and once more information is known we will make a further statement," the post read.
"The team are in a state of deep shock and grief."
Visitors to the zoo were asked to stay in their cars and were temporarily denied entry as Mogli's body was recovered.
PETA spokeswoman Emily Rice said Mogli's death was another reminder that animals do not belong in captivity.
"Even under the best circumstances at the best zoo, wild animals suffer tremendously, both physically and mentally, from the frustration of life in captivity," she said.
"We urge Australians passionate about wild animals to stay away.
"At the end of the day, the paying public can go home, but the animals remain in captivity as living exhibits used to attract crowds until the day they die - often thousands of kilometres from where they truly belong."