More than 40 monkeys were at large in a small US town on Thursday after escaping from a research facility. Authorities warned residents to keep their doors and windows closed.

The rhesus macaques, described as “horrifying” by police in Yemassee, South Carolina, were said to have escaped a day earlier from their enclosures at an Alpha Genesis facility, which specializes in biomedical research on primates.

Search parties were deployed to help locate the monkeys and “lure them with food,” the local police department said on social media.

“Residents are urged to keep their doors and windows securely closed and to report any sightings immediately by calling 911. Please do not attempt to approach these animals under any circumstances,” it said.

Police added that all 43 primates were young females weighing up to three kilograms and that they had not been used for testing.

“An Alpha Genesis spokesperson can confirm that these animals are too young to transmit disease,” it said.

Alpha Genesis CEO Greg Westergaard said the escape was “frustrating” and told CBS News he “hopes for a happy ending” if the primates return of their own free will.

He said the primates were allowed to roam freely after a caretaker failed to secure a door on an enclosure.

“It’s really like following the leader. You see one go and the others go,” Westergaard said.

bjt/des