A group of women doing Tai Chi in a park at sunrise are believed to have discovered a man with fatal stab wounds outside a Sydney train station on Saturday morning.
The stabbing victim, believed to be aged in his 50s, staggered at least 20 metres before collapsing at the Forest Road entrance to Hurstville train station in Sydney's south just after 6am.
Police and paramedics rushed to the scene but could not save the man, who suffered "major trauma" and severe lacerations to his body, police said.
A short time after the man's body was found, a man was arrested at a nearby house, and he is being questioned over the man's death.
Inspector David Ralph, from the St George local area command, said a group of women were doing Tai Chi in the park at the entrance to the station where the man's body was found.
Those women are believed to have raised the alarm, and were due to make a formal statement to police on Saturday.
A bloodied white sheet covered what is believed to be the man's body at the entrance to the train station early on Saturday.
Inspector Ralph said soon after police arrived at the railway station, they received further information "that another male possibly involved was at a home close by".
Police went to that house and arrested a man, believed to be aged in his 20s.
Officers also seized a knife that was believed to have been used in the stabbing.
The man has been taken to Kogarah Police Station, where he is assisting with inquiries. No charges have been laid.
Inspector Ralph said it was not clear whether the men knew each other.
A motive for the incident was also unclear.
"We don't know if it was a robbery, we're not sure of the motive, that's something were looking at," he said.
The Forest Road entrance to the train station has been taped off, but trains are still operating through the station. Police have also set up a crime scene at the house on Patrick Street where the man was arrested.
A neighbour on Patrick Street said two men had moved into the house in the past three weeks.
Forensic police placed markers on a grass area just outside the train station, and a reusable shopping bag could be seen lying at the scene.
The area where the man was stabbed is located along a busy shopping strip, and not far from Westfield Hurstville shopping centre.
Police were asking businesses along Forest Road if they had CCTV footage of the stabbing.
More to come