Japan's Prime Minister Fumio Kishida has been evacuated unharmed from a public event after what appeared to be a smoke bomb was thrown at him.

A person was detained at the scene in Wakayama, where Mr Kishida had been due to give a speech, local media reported.

A witness said they saw a person throwing something, followed by smoke, while another said they heard a big bang.

Video showed officers piling on top of a person, believed to be a suspect.

Police say they have made an arrest, but have so far declined to comment further.

Japan's public broadcaster NHK showed footage in which crowds of people appear to be running away from the scene.

The person detained was arrested on suspicion of obstruction of business, the broadcaster also reported.