A man has been arrested on suspicion of murder after a member of staff at a hospital was stabbed to death at work.
The victim, who has not been named, was attacked at the inpatient unit of Wotton Lawn Hospital in Gloucester at around 7.30am yesterday morning.
Police said the woman was taken to Gloucestershire Royal Hospital but died from her injuries an hour later.
The arrested man is aged in his 60s and is being held in custody, Gloucestershire police said.
A spokesman for 2gether NHS Foundation Trust described the situation as "tragic".
He said: "During the incident a colleague was stabbed and after being attended by fellow clinicians, was taken to Gloucestershire Royal Hospital.
"It is with deep sadness that we confirm that our colleague died a short time later. Our thoughts remain with their family and friends at this extremely difficult time.
"The full facts of this sad incident are still being established and therefore it is inappropriate for us to comment further at this time."
The spokesman was unable to confirm the role of the staff member, but it is understood the woman was not a nurse.
The 2gether website says Wotton Lawn Hospital is an 88 bed acute mental health hospital near the centre of Gloucester which provides inpatient services for the county of Gloucestershire.
The hospital has four admission wards, a nurse led psychiatric intensive care unit (PICU) and a low secure unit (LSU).
It says service users are supported by a variety of healthcare workers including nurses, doctors, psychologists, art therapists, physiotherapists, occupational and sports exercise therapists.
Health Secretary Jeremy Hunt said: "The events in Gloucestershire are devastating and our thoughts are with the family, friends and colleagues of the staff member involved."
People have paid tribute to the NHS worker on social media.
Tania Daniels wrote on Facebook: "I'm in shock. My thoughts are with your family. RIP lovely lady. I'll remember the times you came to my house years ago we had some good laughs and chinwags."
Anastasia Stacie Shields wrote: "She was an amazing lady. It's a real tragedy."
Kerry Louise Daniels wrote: "RIP Hun always in my thoughts. Fly high and shine bright."
Abigail Harris wrote: "RIP my darling angel! Such a lovely lady who will be seriously missed by all the family."
Hayley Robertson wrote: "Awful to happen to a member of the NHS, so sad. Heard all the sirens on the way to work this morning. Can't believe this has happened right outside where I work - such a tragedy. My thoughts and prayers are with the family."
Michelle Sansom added: "Such sad news. RIP poor lady, my thoughts and prayers go to your family and friends and all the staff as well."