A man in his 60s was seriously injured in a knife attack outside the Home Office in central London, police said Thursday.
Another man was arrested nearby and is in custody over the incident, which happened in Marsham Street, Westminster shortly after 1pm local time.
Part of the street was cordoned off and staff inside the Home Office were reportedly told to remain inside.
The injured man was pictured at the scene by Reuters being led away by paramedics.
Police said they were not treating the incident as terrorism but investigators were "keeping an open mind" as to the motive.
It comes only a day after the Home Office launched a campaign against knife crime by printing messages on fried chicken takeaway boxes.
The Metropolitan Police initially described the man's injures as "life-threatening" but later said that his life "is not in danger."
"Officers quickly detained a 29-year-old man near the scene at Smith Square who was arrested on suspicion of grievous bodily harm and possession of CS spray," a police statement said. "He was taken to a central London police station where he remains in custody."
"All my thoughts are with the victim and their family following horrific unprovoked knife attack on Marsham Street," Home Secretary Priti Patel wrote on Twitter.