A 30-year-old woman has died after she was stabbed in an Aldi supermarket in Skipton, North Yorkshire Police said.
The woman was fatally injured in an attack at the store at around 3.27pm on Thursday.
A man of 44 has been arrested on suspicion of murder after being detained by shoppers and staff members at the scene.
A woman who was in the store and asked to remain anonymous said she had "never been so scared in my life".
She heard "loads of screams" then saw the woman lying on the floor and the man pinned down as "everyone screamed and ran up and down" the supermarket.
Police vans arrived on scene within minutes, she added.
Paramedics were also alerted to the store on Keighley Road but the woman died despite their efforts to save her.
North Yorkshire Police said the incident was not terror-related or believed to be a hate crime.
The man was initially arrested on suspicion of attempted murder but the force has now launched a murder inquiry.
The force said the victim's family has been told and they are being supported by officers.
A spokesman said: "We are not in a position to identify the victim at this stage, and we urge people respect her family's privacy and to avoid speculation and rumour on social media."
Officers will remain overnight at the supermarket.
Witnesses and anyone with information are asked to call 101. People affected by the traumatic scene can seek support from the force's Major Incident Response Team by calling 07974745194.