Zookeepers in Australia were pleasantly surprised to discover twin red panda cubs while cleaning an enclosure because they were unaware the mother was pregnant.

Acting senior keeper of pandas at Adelaide Zoo, Lucy Catt, told Xinhua on Wednesday the zoo's "hands-off" approach towards the mother, Imandari, combined with the presence of her one-year-old cubs meant the arrival of young males in January was highly unexpected.

"Firstly, she shouldn't have ovulated anyway and then secondly, was that she has actually birthed a month later than other red pandas have historically done at Adelaide Zoo," Catt said.

"When the cubs are still present, they should inhibit the female from ovulating."

"Towards the end of the year, there were a few behaviors indicative of a potential pregnancy, such as starting to build a nest and those sorts of things," said Catt, but the December breeding season ended with no cubs.

As Imandari was originally destined for release, zoo staff have kept contact with the timid red panda to a minimum and did not notice the mother growing larger. The newborns were found during a routine clean of the night enclosure for Imandari, father Pemba and their first set of cubs.

The nine-week-old cubs, the 45th and 46th cubs to be born at Adelaide Zoo, passed all their vet checks this week and, while they are sticking close to their mother for now, are expected to be on exhibit soon.

Catt also cares for the only two giant pandas in the Southern Hemisphere and said juvenile pair Wang Wang and Funi were improving each breeding season, keeping staff optimistic a successful breeding season was just around the corner.

"They are getting much better with their breeding behaviors," said Catt. "We've already had some fantastic signs from Wang Wang this year," she said.

"(Funi) has just come out of her false pregnancy and this year, for the first time, he was responding to her change in hormones by displaying very dominant behaviors," she added.

She said it was "definitely very exciting" for the upcoming breeding season, which will occur in Australia's winter between July and August.