Prime Minister Fumio Kishida of Japan was safely evacuated on Saturday from a site where he had been scheduled to give a speech and shortly before an explosion was heard, according to the police.
An object was thrown, prompting Mr. Kishida’s removal. By the time of the explosion, the prime minister had been taken away from the area, according to the police department in Wakayama, the western Japanese city where the episode happened. It is not clear what the explosive object was, but it did not result in serious damage or injuries, the police said.
Video footage posted by the national broadcaster, NHK, on Saturday showed police officers, a security detail and what appeared to be members of the public tackling the man the police say is the suspect. The man, who was carrying a gray and black backpack and wearing beige pants, black Adidas sneakers and a blue jacket, appeared to struggle as the police and security officers half-dragged, half-carried him from the scene.
NHK footage showed billowing white smoke rising from a site close to a fishing port where supporters had gathered late Saturday morning to wait for the prime minister to arrive.
Mr. Kishida had been scheduled to give a stump speech in support of a lower house candidate from the ruling Liberal Democratic Party who is running in a special election.
A spokesman for the police department in Wakayama said on Saturday that a suspect had been arrested in the case and was in custody. According to a driver’s license that the police believe belongs to the suspect, he is 24 years old and surnamed Kimura.
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Less than a year ago, former Prime Minister Shinzo Abe was fatally shot during a campaign speech in Nara, a city not far from Wakayama, unsettling a society where gun violence is rare.
Separate video footage on NHK showed the suspect on Saturday holding a slender gray canister shortly before a loud explosive sound was heard.
Mr. Kishida was briefly taken to a police station in Wakayama after he was evacuated from the scene of the explosion. Speaking outside the city’s main train station just over an hour after the episode, he apologized to supporters and vowed to keep on campaigning.
“We are holding an important election for our country, and we must work together with all of you to see it through,” he said.
Toshimitsu Motegi, secretary general of the Liberal Democrats, said it was “an outrage” that the episode had occurred “during the election period, which is the foundation of democracy.” Mr. Abe was killed two days before a general election last July.
Mr. Kishida’s vow to carry on with his schedule echoed a former Japanese emperor, Akihito, who did not suspend events during a visit as crown prince to Okinawa in 1975 after a protester had thrown a Molotov cocktail at the emperor and his wife.
On Saturday, social media lit up with video footage of a man in a long-sleeve red shirt and black-and-white snowflake print vest who appeared to put the suspect in a headlock before police or security officers could get to him. “The old men at the fishing port are more agile and helpful than the Special Police,” one commenter wrote.
Political analysts said that Japan’s sense of public safety could be shaken by more episodes like this one, coming relatively soon after the assassination of Mr. Abe. “Many people believe Japanese society is very safe,” said Tsuneo Watanabe, senior research fellow at the Sasakawa Peace Foundation in Tokyo. “But I think that will not be taken for granted.”
In Japan, political campaigns tend to be relatively loose events where members of the public are allowed to get close to candidates.
But if such episodes continue to occur, security officials might have to become more vigilant and wary of copycats, said Robert Dujarric, co-director of the Institute of Contemporary Asian Studies at the Tokyo campus of Temple University.
“There are always in any country people who have personal gripes or psychological issues or belong to a political group that is fanatically opposed to something the politician does,” Mr. Dujarric said. “And once it’s been done once, you say, ‘Why don’t we try it again?’ ”