A 25-year-old woman was attacked and raped in a Blackpool public bathroom, police said.
Officers were called at 7.25pm on Wednesday.
A woman said she had been attacked by a man in the public toilets off Lonsdale Road.
The toilet block was taped off by police, and witnesses described seeing forensics experts in full protective suits and face masks going in and out of the building at around 4.30pm yesterday.
The woman is currently being supported by specially trained officers.
An investigation is underway and enquiries at an early stage.