A member of the public ran into David Cameron as he left a meeting in Leeds.
The man appeared to collide with the prime minister as he left the city's Civic Hall. Mr Cameron did not fall over and was driven away from the scene, apparently uninjured.
Police took the 28-year-old man away. He was arrested but later released.
West Yorkshire Police later tweeted that no threat had been made, adding: "Nothing sinister, just a man in the wrong place at the wrong time."
The prime minister was in Leeds to launch government plans to upgrade rail links in the north of England.
A member of Mr Cameron's security team intervened and bundled the man away as the prime minister got into a waiting vehicle.
Following the incident, Chief Inspector Derek Hughes said: ''Around midday, a 28-year-old local man was briefly arrested after he came close to the prime minister's group who had just left the civic hall in Leeds.
''No threats were made, and after the man's details were checked, he was de-arrested and allowed on his way.''
The police said they believed the man was sprinting to a nearby gym.
The BBC's Tom Symonds said a member of David Cameron's party told him that the prime minister stepped back as the man ran towards him and was not in contact with him.
