A woman was found in a bath with multiple stab wounds in Adlington.
A neighbour of the 30-year-old female raised the alarm at 1pm on Wednesday.
Police officers and paramedics found the woman unconscious with numerous deep slash wounds.
Insp David Robinson of Chorley Police said: “The female had been self-harming with a knife and was found lying in the bath with multiple, deep slash wounds.
“It is also believed that she may have consumed harmful fluids, including bleach, and when the officers arrived at the address in Adlington the woman was showing very little signs of life. They administered CPR and kept her alive until the paramedics arrived and transferred her to Chorley A&E.”
The woman, who has not been named, is believed to still be in a serious condition in hospital.