More than 5,000 visitors were asked to leave the 110-acre Chester Zoo shortly after chimps found their way into a keeper area where their food is prepared.
There were no injuries to members of the public or staff and the decision was taken purely as a precautionary measure, the zoo said in a statement.
“We apologize for any inconvenience this has caused to our visitors and would thank them for their full co-operation and patience,” the statement said.
The zoo has more than 1.3 million visitors a year and has been named by Forbes as one of the best 15 zoos in the world.
Sarah Jones, from Chester, was among the visitors at the zoo when the animals left their enclosure.
“My two young boys had only just gone into the chimpanzee house when we heard terrifying loud noises,” she said.
“The chimpanzees were large animals and they seemed very upset about something, they were making a frightening noise, I thought something was wrong, so we made our way out of the building.
“I saw keepers running into the house and visitors were asked to head to other areas of the zoo.
“We ended up being stuck in the cafe area for quite a while.” [via]