A man stabbed on a train station concourse has died, police said.
The victim, in his 40s, was taken to hospital with life-threatening injuries following the stabbing at Plymouth station, but later died.
A 29-year-old man has been arrested on suspicion of murder and is in police custody.
British Transport Police said it was working to identify the man and inform his family and appealed for any witnesses to come forward.
Det Ch Insp Paul Langley said: "This was an attack on a man in broad daylight at a busy station in Devon.
"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.
"The victim was taken to hospital but he sadly died despite the best efforts of the medical teams."
A spokesman for South Western Ambulance Service said paramedics attended to two male casualties, one with minor injuries and another with head and shoulder injuries.
The ticket office of the station has been closed off due to the incident, leaving passengers unable to buy or collect reserved tickets.
A spokesman for Great Western Railway 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."
Network Rail said trains were "running as normal".