At an outdoor event, the Japanese Prime Minister was present. A loud explosion could be heard.
Japanese media claimed that a pipe-like item was thrown towards Fumio Kishhida and appeared to be smoke bomb.
The incident occurred shortly after the leader began to speak at a Wakayama port. He was then evacuated.
NHK reports that the man remained uninjured and took cover during the incident.
A news reporter reported that an eyewitness saw a flying object, and added: “It made me feel bad, so we ran very fast.” We then heard a loud noise. My daughter cried.”
The footage showed uniformed police officers pressing a man to the ground as the crowd fled. Later, the police confirmed that an arrest was made.
Shinzo Abe, the longest serving leader of Japan, died in July after being stabbed at close range during a speech for a political campaign outside a station.
The assassination shocked a nation and led to a review of the security measures for politicians.
Mr Kishida visited the area to encourage one of his candidates who was taking part in local elections.