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.

There is a animal research facility on RPA hospital grounds.

The baboons were contained by police and medical experts before handlers from Taronga Zoo tranquillised them.

NSW Health Minister Brad Hazzard told AAP there was a lock failure either on the truck or crate that was transporting a 15-year-old male and two females.

"The three baboons decided to take a bit of a look around RPA grounds," he said on Tuesday.

"They didn't know what to do nor did the people around them."

Mr Hazzard insisted the baboons were not being transported for research purposes and the male was at the facility for a vasectomy.

"It had been decided the male needed to have a vasectomy to continue to move with his female troop and not keep producing babies," he said.

"If he had been kept fertile he would have had to moved from the family he knows."

The health minister said the baboons should be awake and well a few hours.

The male baboon is due for the vasectomy on Wednesday and the females are with him to "keep him calm".

The minister added that baboons are part of research programs that cover a whole range of health issues but when they are finished with the program, they're always returned to their colony.

NSW Police had earlier said there was no immediate danger to the public but that people were advised to avoid the area.

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

Animal activist and former GP Kevin Coleman said the primates' escape was a "major concern" 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 said he believes experts are undertaking research into human-baboon hybrid organs to address the transplant crisis.

Mr Hazzard dismissed these claims succinctly.

"It's rubbish," he said.

"These baboons were simply there for the old vasectomy," he said.

Australian Associated Press