A man has died after being stabbed on the concourse at Plymouth railway station.
British Transport Police, Devon and Cornwall Police and South Western Ambulance Service were called to the scene at 10am on Tuesday.
The victim, a man aged in his 40s, was taken to Derriford Hospital in Plymouth for treatment but died.
A 29-year-old man has been arrested on suspicion of murder and the station has been cordoned off.
Detective Chief Inspector Paul Langley, of British Transport Police, said: “This was an attack on a man in broad daylight at a busy station in Devon.
“We are now working to identify the man and inform his family.
“At this time, it is believed the two men knew each other and had an argument at the station, which resulted in one of the men assaulting the other.
Any witnesses please call 0800 40 50 40 or text 61016— BTP Devon & Cornwall (@BTPDevonCorn) August 8, 2017
“The victim was taken to hospital but he sadly died despite the best efforts of the medical teams.
“We are now asking anyone who may have been at Plymouth station this morning and witnessed what happened to come forward and speak to us.
“Any information, no matter how small, could prove vital in our inquiries.”
Mr Langley said BTP and Devon and Cornwall Police will have extra officers in the area in the coming days.
“Thankfully, assaults such as this are very rare and we are doing everything to establish what has happened,” he added.
The arrested man was initially taken to hospital for treatment to a hand injury.
A spokesman for South Western Ambulance Service said paramedics were called at 9.58am.
They attended to two male casualties, one with minor injuries and another with head and shoulder injuries.
“We attended with two ambulances and one rapid response vehicle,” the spokesman said.
“Both casualties were taken in to Derriford Hospital for treatment.”
The ticket office of the station has been closed off due to the incident, leaving passengers unable to buy or collect reserved tickets.
Network Rail said trains were “running as normal”.
A spokesman for Great Western Railway (GWR) said: “Access to Plymouth Station is restricted and the ticket office remains closed while police continue to investigate the incident this morning.
“The station remains open, with tickets available on platforms and on-board trains.”
Luke Pollard, MP for Plymouth, Sutton and Devonport, tweeted: “Disturbed to hear about the stabbing at #plymouth train station. If you saw anything please contact the Police.”