Detectives are appealing for witnesses following an incident in Moor Row, west Cumbria.
Police received a report of the rape of a girl, aged in her late teens, at a path near the junction with Dalzell Street.
She is being supported by officers.
Police are investigating and are appealing for anyone who may have seen anything suspicious at the time – at about 3.30pm to 5.30pm on Saturday October 31, which was Halloween.
Officers received the report on Friday (November 13).
Detective Chief Inspector Matt Scott said: “We have a team of detectives who have spent the last few days conducting numerous enquiries, which are at an early stage.
“Incidents such as this are very rare but the community can take reassurance that we are doing all we can to investigate this.
“We will also have regular reassurance patrols out in the community, so residents may be aware of a larger than normal police presence.
“The victim is being supported by officers.
“This investigation is in its early stages but we feel the public could help us with information, so we are appealing directly - and I would encourage anyone with any information to please contact us as it may assist our investigation.”
Officers are keen to trace a man who was described as a white male, more than 5ft 9ins tall, with a greasy fringe covering his forehead, and of a large build.