MANCHESTER, United Kingdom (AFP) — A British police probe into a triple stabbing at a Manchester railway station on New Year’s Eve which injured three people is now being treated as “a terrorist investigation”, the city’s top officer said on Tuesday.

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 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,” 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.”

No group has claimed responsibility for the attack, which happened at around 8:50 pm (2050 GMT) 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’.”

Clack also quoted the suspect as saying: “As long as you keep bombing other countries, this sort of shit 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 blade.

“It was just fear, pure fear.”

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.