A mother has been discovered lying in a pool of blood - her nine-month old baby daughter was beside her screaming.
Police have now arrested a man on suspicion of murder, although the woman, aged 33, has not yet been named.
She died yesterday morning at around 9am in north-west England.
Lancashire Police confirmed they were called to the house after concerns were expressed about the safety of the mother.
The baby was unharmed.
On Saturday, a 34-year-old man ‘known to the victim’, detained earlier on Friday for being in possession of a knife, was being questioned on suspicion of murder.
A post-mortem examination is expected to be conducted shortly.
A police spokeswoman said: “We have launched a murder investigation following the death of a woman in Burnley.
“At around 9am on Friday, July 22 a man was stopped in Holmby Street after he was seen acting suspiciously.
“He was arrested on suspicion of possession of a knife and taken to custody.
“Shortly after 9.30am officers attended an address in Wilton Street to check on the safety of a woman.
“A 33-year-old woman was found inside the address and was sadly pronounced deceased at the scene.
“A seven-month-old baby girl was also found at the address unharmed and has been taken to a place of safety.”
Detective Inpector Andy Cribbin, of the Force Major Investigation Team, added: “This is a tragic incident involving the death of a woman and we are in the very early stages of a murder inquiry.
“At this stage we believe it to be an isolated incident and currently have one man under arrest.
“Our enquiries remain on-going and I would urge anyone who may have any information that could assist with our investigation to contact us as soon as possible.”