Siam, the oldest elephant held in captivity in Australia, has died on Tuesday due to kidney failure.

But staff and volunteers at the Australia Zoo said Siam's death was something they know would happen anytime soon since the animal was almost 60 years old. They had been monitoring her health.

"It was not totally unexpected because she is quite an older animal, obviously, but it's pretty hard whenever anyone in your family passes away," Kelsey Engle, curator of Australia Zoo, told reporters. Siam was found dead in the early hours of the morning.

The zoo did however say it is quite baffled as to the cause of death since Siam bore no indication of any kidney problems.

Siam, the largest of three Asian elephants the zoo has in captivity, came to Australia Zoo in 2003 to live out her retirement after being part of a travelling circus. The other two were Bimbo and Sabu.

"As the largest of our three Asian elephants, she was affectionate, cheeky and endearing," the zoo said in a memo to staff and volunteers. "She will be sorely missed."