London police said on Tuesday they had arrested a man who was carrying an axe on The Mall, which connects Buckingham Palace with Trafalgar Square, but there were no reports of injuries.
The Metropolitan Police said officers on patrol on The Mall saw the man about 6.30pm on Tuesday.
"Armed officers were on duty near by," police said. "They attended the scene where the male, believed to be in his 40s, was detained and arrested on suspicion of carrying an offensive weapon."
Photos from witnesses on Twitter showed officers surrounding the man near the Institute of Contemporary Arts building.
The man remains in custody at a central London police station.
Enquiries are ongoing and the incident is not being treated as terror-related.
