Visitors to the Belfast Zoo in Northern Ireland managed to get a lot closer to the chimpanzees than they were expecting to on Saturday (Feb 9).
Several chimpanzees climbed up to the top of the wall of their enclosure with the help of a large tree branch, and one was seen along a public footpath in the zoo, going by footage posted on social media.
Ms Danielle Monaghan - who was at the zoo with her children, her partner and his nieces - witnessed the primates' escape, the BBC reported.
She said that she was "petrified" when one of the chimps climbed out of the enclosure and started walking around it. However, the animal did not seem threatening, to Ms Monaghan's relief.
"It may have been a different story if it had been aggressive but it absolutely wasn't. It made us feel at ease. We just walked past it and it was absolutely grand," she told the BBC.
Belfast Zoo spokesman Alan Cairns said that the trees in the chimpanzees' enclosure were likely to have been weakened by recent storms, allowing the apes to break a tree branch and use it as an improvised ladder.
However, the zoo's chimpanzees were "quite cowardly" and later returned to the enclosure on their own.
"They're intelligent primates and know they're not supposed to be out of their enclosure, so got back in themselves," he told the BBC.
Mr Cairns told the British broadcaster that the zoo will review the design of the enclosure, and may have to remove the trees, although they do not want to do so.
Last month, an endangered red panda cub escaped from Belfast Zoo.It was eventually found in a residential garden a short distance from the zoo.
In November last year, a snow leopard was shot dead after the animal escaped from its enclosure in Dudley Zoo in Britain.
A zookeeper had left the enclosure door open, and the eight-year-old snow leopard was killed in the interest of public safety, the zoo said.
Last June, two lions, two tigers and a jaguar escaped their enclosures in a flooded German zoo for several hours. Local residents near the Eifel Zoo were told to stay indoors while the big cats were on the loose.