Hong Kong police said it had detained a man responsible for attacking a Japanese couple, underlining the mounting anti-Japanese sentiment ignited by tensions over territorial disputes.

The Japanese consulate issued a warning soon after the attack, urging expatriates to stay off the streets, particularly at night. According to reports, the Japanese couple, aged 37 and 35, were strolling on a busy waterfront when a man attacked them with several punches and fled the scene. The man allegedly asked the couple whether they were Japanese before assaulting them. A police spokesman told AFP that they arrested a 31-year old Hong Kong man on Tuesday for questioning over the assault. He is required to report to the station later this month.

This comes as increasingly violent protests broke out across China after Tokyo announced that it had nationalized several islets from the Senkaku chain. Japanese companies were also forced to close up shop as hundreds of protesters took to the streets.

Tensions have escalated following the arrest of Hong Kong activists who attempted to plant a Chinese flag on the island in the East China Sea. US Defense Secretary Leon Panetta warned that “provocative behaviour” could embroil the Asian countries into war. Mr. Panetta met with Chinese Defense Minister Liang Guanglie in Beijing but touched on other regional issues.