Dutch police launched an investigation on Thursday into the overnight theft of 12 rare monkeys from an animal park in central Netherlands which has left zoo workers fearing for the tiny primates' lives.

The brazen burglary was discovered around 9:00 am (0800 GMT) when a worker of the Wissel Dierenpark near the town of Epe, about 100 kilometres (60 miles) east of Amsterdam, went to check on the primates.

"He saw a wooden door leading to their enclosure had been forced open," Wissel's spokeswoman Bernou Wagenaar told AFP.

Upon investigation the worker found "that some of our rarest monkeys had been stolen," she added, saying police were immediately notified.

The haul included six silvery marmosets, three pygmy marmosets, a breeding pair of golden lion tamarins and one cotton-headed tamarin.

Both tamarin species are considered highly endangered and feature on the Convention on International Trade in Endangered Species' (CITES) Appendix I, said Wagenaar, meaning they are threatened with extinction and commercially trading them is forbidden.

Wagenaar said a team of police investigators have been sent to the animal park "and they are still on the scene."

Park said they worried the tiny monkeys, all tropical species, may not be able to withstand the sudden change from a warm cage to the cold Epe night, where temperatures plummeted to minus three degrees Celsius (27 degrees Fahrenheit) early Thursday, according to local media reports.

The monkeys also have a highly specialised diet that requires a mix of fruits, insects and a vitamin supplement, said Wagenaar, who added the park could not put a price tag on the loss of its most valuable primates.

Police spokeswoman Liesbeth Oelen confirmed police were investigating, saying: "It's clear that the thieves specifically targeted these monkeys."