A school was "locked down" as armed police launched a search after a teenager was seen with a knife near a school. 

Armed officers swooped on Sherborne yesterday after after a man was reportedly seen around 1.40pm carrying a knife in Acreman Street. 

The man then walked off toward the town. 

Sherborne Preparatory School, which is on Acreman Street, said triggered a lock down procedure as a precautionary measure.

Officers, including armed officers, were sent to the scene and a search of the area was carried out.

A 17-year-old boy from Sherborne was arrested in the town centre on suspicion of possessing a bladed article in a public place and public order offences.

The teenager is assisting officers with enquiries.

No one was injured during the incident.

Headmaster of Sherborne Prep School, Nick Folland said: "Sherborne Prep was informed of a youth who had been observed acting suspiciously and suspected of carrying a knife on the lane adjacent to the school. 

"As a precautionary measure the Prep School enacted its 'lock down' procedure and informed parents of the incident and its management. 

"I am extremely proud of both the staff and children who acted calmly and professionally in accordance with our policy and training."