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 video also shows people swarm around one man, hold him down, and then carry him away.

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

Mr Kishida had just started to deliver a speech after touring the fishing harbour in Wakayama when the object was thrown and he took cover.

A woman at the scene told NHK: "I was stunned. My heart is still beating fast."

Another witness told NHK that the crowd began to disperse in panic before the blast was heard, as someone said an explosive had been thrown.

Hiroshi Moriyama, a member of Mr Kishida's Liberal Democratic Party, said: "That something like this happened in the middle of an election campaign that constitutes the foundation of democracy is regrettable. It's an unforgivable atrocity."

The incident comes after former Prime Minister Shinzo Abe was shot dead while on the campaign trail last year. (BBC)

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