A 20-year-old man was arrested Sunday after allegedly throwing a flare at the building housing the Chinese Consulate General in Nagasaki, they said.
The incident, apparently linked to Japan's diplomatic spat with China over the arrest of a fishing boat captain near islands administered by Japan but also claimed by Beijing and Taiwan, occurred at 9:25 a.m.
Police identified the man as Kazuki Tanigawa, a member of a private political group. No one was injured because the consulate is closed on Sundays, they said.
The man was taking part in a political rally near the consulate with his fellow members, according to police.
In a related development later in the day, a man on a scooter fled after apparently setting a piece of paper on fire outside the building of the Chinese Consulate General in Fukuoka, local police said.
Sunday's incidents followed the arrest of another man with a knife outside the Prime Minister's Official Residence on Saturday.
Masaki Watanabe, a 32-year-old unemployed man from Osaka, told police he wanted to protest the release of the skipper. He was carrying a statement of protest, the police said.
He was allegedly carrying a 17-cm-long kitchen knife in a bag in front of the office, a violation of the Sword and Firearm Control Law.
The suspect told police he was carrying the knife for self-defense.