Three baboons that escaped a Sydney hospital have been contained by police and medical experts.

Police were called to a car park near Royal Prince Alfred Hospital on Missenden Road and Lucas St in Camperdown about 5.30pm on Tuesday after the baboons escaped while being transported, a NSW Police spokeswoman told AAP.

"They're currently contained and police are working with experts to safely return them to their facility," the spokeswoman said.

"There is no immediate danger to the public but people are advised to avoid the area."

Footage shared on social media shows three baboons running in the car park as people stop and take a surprised double-take.

There is a medical research facility within RPA hospital where it's believed testing is done on animals.

Animal activist and former GP Kevin Coleman says it's a "major concern" the primates escaped which could raise biosecurity issues.

"If an animal the size of a baboon can escape, how many mice have escaped, how many other animals have escaped?" he told AAP.

"We just don't know and this is the problem. We have to have transparency on these issues."

The Sydney Save Animals in Laboratories spokesman says he believes experts are undertaking research into human-baboon hybrid organs to address the transplant crisis.

NSW Health has been contacted for comment.