MANCHESTER (AFP) - A British police probe into a triple stabbing at a Manchester railway station on New Year's Eve that injured three people is now being treated as "a terrorist investigation", the city's top officer said on Tuesday (Jan 1).

Counter-terrorism officials have arrested a man who remains in police custody, and are searching an address where he recently lived in the northwestern English city, Chief Constable Ian Hopkins said.

The suspect reportedly shouted "Allah" during what Chief Constable Hopkins called a "horrific attack" on three people, including a police officer, at Manchester Victoria station on Monday evening.

A man and a woman, both in their 50s, are still being treated in hospital after sustaining "serious" injuries, while the officer was also stabbed in the shoulder, he added.

"We are treating this as a terrorist investigation, which is being led by counter-terrorism officers with support from Greater Manchester police," Chief Constable Hopkins told a briefing.

"They were working through the night to piece together the details of what happened and to identify the man who was arrested," he said, adding that an address in the Cheetham Hill area of the city was being searched.

Prime Minister Theresa May thanked emergency services for their "courageous response".

She wrote on Twitter: "My thoughts are with those who were injured in the suspected terrorist attack in Manchester last night."

'PURE FEAR'

No group has claimed responsibility for the attack, which happened at around 8.50pm when many revellers in the city would have been enjoying New Year's Eve celebrations.

Witness Sam Clack, 38, a BBC radio producer, said he heard the suspect shouting "Allah" before and during the attack.

He added: "He shouted it before, he shouted it during it - 'Allah'."

Mr Clack also quoted the suspect as saying: "As long as you keep bombing other countries, this sort of s*** is going to keep happening."

The witness said he heard the "most blood-curdling scream" and looked down the platform to see the attack unfolding.

"He came towards me," he added. "I looked down and saw he had a kitchen knife with a black handle with a good 12 inch (30-centimetre) blade."

"It was just fear, pure fear."

Mr Clack said police officers used a stun gun and pepper spray before "six or seven" officers jumped on the man.

Video footage of the incident shows the male suspect being overpowered by the officers.

Manchester police said he was arrested on suspicion of attempted murder.

The woman suffered injuries to her face and abdomen and the man was wounded in the abdomen, while a British Transport Police officer sustained a stab wound to the shoulder.

Their injuries were described as serious but not life-threatening.

'DREADFUL'

The city's New Year celebrations went ahead in Albert Square despite the incident, with a firework display taking place as planned, though increased security was brought in.

The city experienced a suicide attack in May 2017, when 22 people were killed and 139 wounded at a concert by the US singer Ariana Grande at the Manchester Arena.

The bomber, Salman Abedi, 22, was born and raised in Manchester.

"I know that the events of last night will have affected many people and caused concern," Chief Constable Hopkins said on Tuesday.

"That the incident happened so close to the scene of the terrorist attack on May 22, 2017, makes it even more dreadful. Our work will continue to ensure we get to the full facts of what happened and why it took place."