Police arrested a 31-year-old Hongkonger over an assault on a Japanese couple in Tsim Sha Tsui on Monday night.
Officers caught the man in Hung Hom at about 11pm on Tuesday with the help of closed-circuit television footage. He was released on bail and must report back to police next Thursday.
The attack prompted the Japanese consulate in Hong Kong to post a notice on its website the day after, warning its 22,000 citizens to avoid deserted places at night, a spokeswoman for the diplomatic mission said. "We would also like to remind Japanese to stay away from protests if they see any," she said.
Police said frontline officers had been told to pay more attention to Japanese-related department stores, restaurants and other businesses.
The attacker struck at about 8pm as businessman Tatsuya Akioka, 37, and his wife, Miwa, 35, walked along the Tsim Sha Tsui East promenade from their home in Hung Hom.
He approached them and asked in English if they were Japanese. He then punched them and fled. The couple were treated at Queen Elizabeth Hospital in Yau Ma Tei for minor injuries to their legs, shoulders and heads, and were discharged.
Akioka is understood to be the general manager of a Japanese fashion company in Hong Kong.
Meanwhile, police are investigating a bomb hoax at the Japanese consulate general in One Exchange Square, Central. A caller phoned in the threat yesterday afternoon.
Two Hongkongers have sued Japan over the Diaoyus, known as the Senkaku Islands in Japan.
Diaoyus activist Lo Chau returned to Hong Kong yesterday after filing a lawsuit with the Supreme People's Court in Beijing.
Lo is suing the Japanese government for detaining him and fellow activists after they sailed to the islands last month, and for charging them with the crime of illegal entry. He is seeking compensation for damage to his boat.
The judge said the court would look into the case but did not say whether it would accept the suit, Lo said.
Another man, Chan Yuk-lun, filed a writ in Hong Kong asking the High Court to declare that the East China Sea islands belonged to China.