POLICE in Launceston are seeking the public's help following a serious sexual assault which took place in the town in the morning Tuesday, July 23.

A 17-year-old local girl was subjected to the attack in an alleyway in Tower Street sometime between 9.30am and 11am.

Police are appealing for any witnesses who may have seen a stocky white man, in his 30s, wearing a dark shirt, blue jeans and sandals in the vicinity.

A police spokesman said: "This type of attack is a very rare occurrence for Devon and Cornwall and we are determined to identify the person responsible as soon as is possible.

"We would like to hear from anyone who was in the area at the time and noticed anything suspicious at all."

Police have stepped up community reassurance patrols in the area and a team of detectives are working on locating the offender.

Anyone with any information is asked to call police on 101 or Crimestoppers.