Scotland Yard has said it is keeping an open mind over the motive for a knife attack outside the Home Office as it was confirmed that the victim is a government employee.

Specialist firearms officers attended within six minutes to find a man in his 60s with knife injuries, the Metropolitan police said. The man’s injuries were neither life-threatening or life-changing, the force said.

The government confirmed that the victim is a civil servant at the Ministry of Housing, Communities and Local Government (MHCLG), which is in the same building as the Home Office in Marsham Street, Westminster.

The communities secretary, Robert Jenrick, called the incident a “horrific attack on a colleague”.

The home secretary, Priti Patel, tweeted: “All my thoughts are with the victim and their family following horrific unprovoked knife attack on Marsham Street.”

A 29-year-old man was arrested outside St John’s church in nearby Smith Square on suspicion of grievous bodily harm and possession of a CS spray.

Video obtained by the Sun appears to show the suspect being arrested and items left at the scene, including a rucksack and a box containing a live ferret.

Photos posted on social media showed police tape and several officers outside the building.

Lots of armed police and a cordon going up outside the Home Office pic.twitter.com/aj0RqDnPsm — Gareth Milner (@sw1a0aa) August 15, 2019

A Reuters photographer captured images of a man holding a cloth to his face being escorted away from the building by a paramedic and armed officers.

An office worker opposite the Home Office, who asked to remain anonymous, described seeing a man – thought to be the perpetrator – walking calmly down the road after the incident.

She told PA Media: “He was standing over there outside the Home Office and then he was putting something away in his bag, but I didn’t see a knife or anything. He was putting something away and then he just calmly just walked off down the road as if nothing had happened. Then people were being asked to go into the Home Office; they were being ushered in.”

A barista working opposite the Home Office said she saw the victim walking out of the government building. The witness described him as a man who appeared to be in his 50s. “He had just trousers, nothing on top ... He was full of blood. He was escorted by police and paramedics.”

London Ambulance Service attended the address and took the victim to a central London hospital. The injured man’s family have been notified.

The Met said: “Inquiries are ongoing to establish the circumstances of the incident. We are keeping an open mind about any possible motive at this early stage.”

Jenrick said: “I am deeply shocked by this horrific attack on a colleague today. My thoughts, and those of all my staff, are with him and his family. We are ready to provide as much support as we can and we all wish him a speedy recovery.

“We will be reviewing security across the MHCLG estate. All our staff must feel safe as they go about their important work. I would like to give my heartfelt thanks to the police, ambulance service and our staff for their swift response today.”

A spokeswoman for the Home Office said: “The Metropolitan police is investigating a knife attack which took place outside the Home Office this afternoon. The victim is receiving medical care. This is a deeply concerning incident and our thoughts are with him and his family. As this is an ongoing investigation, it would be inappropriate to comment further.”