LONDON (AP) — Visitors at an English zoo have been evacuated after police and an air ambulance were called to deal with an incident.

Cambridgeshire Police said Monday the force responded to a call indicating that a "serious incident" was in progress at Hamerton Zoo, 80 miles (130 kilometers) north of London.

Police said the public was not at risk and no animals had escaped but did not elaborate. The incident took place on a British holiday when children are off from school.

Witness Jeff Knott told Britain's Press Association the staff was very professional and the visitors departed the zoo "in a very calm manner — no running, shouting or anything similar."

Police said more details would be made available later.