Counter-terrorism police have launched a major investigation following the savage attack in Manchester.
A British Transport Police spokesman said earlier a man and a woman - both in their 50s - were taken to hospital.
The woman had injuries to her face and abdomen and the man had injuries to his abdomen.
A BTP officer was also attacked and suffered a stab wound in his shoulder. The officer was later released from hospital.
The injuries to the man and woman were described as serious but not life-threatening.
Sam Clack, a BBC producer, was waiting on a platform at Manchester Victoria railway station waiting for a tram when he witnessed the attack.
Mr Clack, 38, said: “I just heard this most blood-curdling scream an looked own the platform.
“What it looked like was a guy in his 60s with a woman of similar age and another guy all dressed in black.
“It looked like they were having a fight but she was screaming in this blood-curdling way.
“I saw police in high-vis come towards him.
“He came towards me. I looked down and saw he had a kitchen knife with a black handle with a good 12-inch blade.
“It was just fear, pure fear.”
Mr Clack, on his way to catch a tram home, said officers used a Taser and pepper spray before, “six or seven” officers jumped on the man.
The BBC producer, from Newcastle, said the suspect was held down, he said: “As long as you keep bombing other countries this sort of shit is going to keep happening.”
He said it looked like both the man and the woman with him had been stabbed but both were conscious and blood-curdling to a waiting ambulance.
BTP said they were called at 8.52pm to reports of a man with a knife who has 12-inch.
Two members of the public have been taken to hospital with knife injuries and a BTP officer is being treated for a knife wound to the shoulder.
The station remains closed and officers are at the scene, police said.
Assistant Chief Constable Rob Potts said the investigation was being led by counter-terrorism police and officers were keeping an "open mind".
He said: "Tonight's events will have understandably worried people but I need to stress that the incident is not ongoing, a man is in custody and there is currently no intelligence to suggest that there is any wider threat at this time."
It is next door to Manchester Arena which was the scene of a deadly terror attack at an Ariana Grande concert in May 2017.
Salman Ramadan Abedi, a 22-year-old local man of Libyan ancestry, detonated a suicide vest – killing 23 people and injuring 139, many of them children.
It was the deadliest attack and the first suicide bombing in Britain since the July 7, 2005 London bombings.