Chimpanzees used branches felled by a storm to escape from their zoo enclosure, in front of witnesses, who filmed the whole episode.
This was the second escape in as many months from Belfast zoo, after a red panda escaped in January and was found in a garden less than 1.5km away.
Visitors said they saw the escaped chimps emerge from the bushes on to a path, as others sat on top of their enclosure wall.
Zookeeper Alyn Cairns blamed the recent storm for the escape, but told the BBC that the chimpanzees did not enjoy their taste of freedom.
He said: "They're intelligent primates and know they're not supposed to be out of their enclosure, so got back in themselves."