A man was seriously injured after being stabbed in front of the Ministry of the Interiorin the Westminster district of central London, police said on Thursday.
The victim's days are in danger, the police said in a statement.
A suspect arrested
"A man was arrested, suspected of causing serious bodily harm, and taken to the police station," the police added, saying that they still had to determine "the exact circumstances" of the attack.
The police, who were alerted shortly after 13 hours local (12 hours GMT), cordoned off the area. A photo broadcast by British media shows a man escorted by the emergency services, the bloody face covered with a rag.
He is shirtless, a suit jacket placed on his shoulders, and his belly covered with blood. Contacted, the Interior Ministry did not comment.