An elderly man is in a life-threatening condition after emergency services were called to Hilsea station this morning.
Police cars were spotted parked along Norway Road by the station, while an air ambulance has also been at the scene.
It is believed that a man suffered a suspected cardiac arrest and fell over.
Police sent several cars as a precaution.
A South Central Ambulance Service spokeswoman said a call was received at 10am and paramedics attended a medical emergency at the station.
She added that an elderly man had been assessed and taken to the QA Hospital in a life-threatening condition.
A British Transport Police spokesperson said officers were called at 10.02am following reports a man had collapsed on the platform.
The incident is not being treated as suspicious.
John Hook, a passenger waiting for a train at the station was told by an eyewitness that the man collapsed and hit his head on the platform.
He said: ‘A lady who saw the whole thing said she saw an elderly man sat down at the station and then suddenly lean forward and hit his head.
‘She said there was blood everywhere and that it was a suspected heart attack.
‘I arrived at the station just after and there were about five or six police cars.’