A Swedish zoo said on Thursday it had to shoot dead three chimpanzees after they escaped from their enclosure, with the situation still not under control.

A fourth primate was injured by gunshot, according to the company that runs the Furuvik Zoo around 200 kilometres north of Stockholm.

"A chimpanzee is considered a high-risk animal. If this kind of animal gets out into the zoo, it can pose a threat to people's lives", said Annika Troselius, a spokeswoman for Parks and Resorts.

Five of the zoo's seven chimps managed to escape from their enclosure on Wednesday shortly after noon (1100 GMT), and were roaming freely around the zoo.

It is not yet known how they escaped.

The zoo is currently closed to visitors for the season, but staff were either evacuated or ordered into safety indoors.

The decision to shoot dead the chimps came in for harsh criticism on social media sites.

According to the zoo, tranquilising the animals "was not an alternative".

"In order to fire an anaesthetic dart, you need to be very close to the animal. In addition, you have to wait up to 10 minutes for the tranquiliser to take effect", the zoo said in a statement.

On Thursday afternoon, the zoo's four surviving primates were in the monkey building but had not yet returned to their enclosure, Furuvik Zoo wrote in an update on Facebook.

"This means that we can't let people move freely inside the zoo and we are still on high alert", the zoo said.

The chimps' escape comes on the heels of several other high-profile evasions in Sweden.

At the end of October, a king cobra slithered out of Stockholm's open-air museum and animal park Skansen and was missing for about a week until it returned on its own.

A month later, two great grey owls escaped from the aviary at the same zoo but have since flown back. (AFP)