Worries were compounded as Hainan is technically the province which has jurisdiction over China's extensive South China Seas claims, raising the possibility Chinese police could board ships anywhere in those waters.
But Chinese Foreign Ministry spokeswoman Hua Chunying said the scope of Hainan's rules, announced by state media in November, represented no change from regulations passed in 1999 limiting enforcement to within 12 nautical miles of Hainan's coast.
"What I want to stress is that these local rules were formulated by the Hainan provincial government to strengthen border controls over the coast and maritime management," Hua told a daily news briefing.
"Their aim is to tackle crime at sea and maintain peace on the seas. There is no change to the scope of how these rules are used compared to the 1999 rules," she added, without elaborating.