Japanese Prime Minister Fumio Kishida resumed campaigning on Saturday after being evacuated unharmed from the scene of an apparent "smoke bomb" blast.
The incident in western Japan's Wakayama came less than a year after the assassination of former prime minister Shinzo Abe, which traumatised the country and forced a security shake-up for public officials.
Mr Kishida was in the city to deliver remarks in support of a ruling party candidate and had just finished sampling fish at a local port when a disturbance rippled through the crowd gathered to hear him speak.
Footage from national broadcaster NHK showed the prime minister turning to look backwards as a person was detained by security and people moved away, some shrieking.
Seconds later, a blast was heard and white smoke filled the air.
Local media reports showed a silver, pipe-like object on the ground, but it was not immediately clear whether it had caused the blast and smoke.
NHK said a man had been arrested at the scene on suspicion of obstruction of business.
A man at the scene told the broadcaster that "when we all stopped in front of the podium, someone started saying 'culprit!' or something, or 'an explosive was thrown,' so everyone started dispersing fast."
"And then, about 10 seconds after the culprit was captured, there was a blast," he said.
Mr Kishida was unharmed, and soon resumed campaigning, including a stop at a local train station.
"There was a loud blast sound at the previous speech venue. Police are investigating details, but I'd like to apologise for worrying many people and causing them trouble," Mr Kishida said.
"An election that's important to our country is taking place, and we must work together and follow through on it."
He was also due to visit Chiba, east of Tokyo, later on Saturday.
"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," Hiroshi Moriyama, the ruling Liberal Democratic Party's election strategy chairman, told NHK.
Security at local campaign events in Japan can be relatively relaxed, in a country with little violent crime and strict gun laws.
But the country bolstered security around politicians after the assassination of Mr Abe, who was shot and killed while speaking at a campaign event in July 2022.
His alleged assassin, Tetsuya Yamagami, reportedly targeted him over his links to the Unification Church, and the incident sparked revelations about the connection between the sect and political figures in Japan.
Yamagami was reportedly angry at the sect over large donations his mother made to the group that left the family bankrupt.
The head of Japan's National Police Agency, and the local police chief, resigned after an investigation confirmed "shortcomings" in Mr Abe's security.
The investigation criticised a system under which local police were given responsibility for the security of visiting senior officials.
With proper security, "it is deemed highly probable that this incident could have been prevented", the report concluded.
Saturday's incident comes as Group of Seven climate and energy ministers meet in the northern city of Sapporo, and a day before G7 foreign ministers arrive in Karuizawa in Nagano for talks.
Japan will host the G7 leaders' summit next month in Hiroshima.
