Kham/Reuters
Fishing boats off Vietnam’s coast in the South China Sea. One Chinese official said the new rules applied to disputed islands, too.
HAIKOU, China — New rules announced by a Chinese province last week to allow interceptions of ships in the South China Sea are raising concerns in the region, and in Washington, that simmering disputes with Southeast Asian countries over the waters will escalate.
The move by Hainan Province, which administers China’s South China Sea claims, is being seen by some outside analysts as another step in the country’s bid to solidify its claims to much of the sea, which includes crucial international shipping lanes through which more than a third of global trade is carried.
As foreign governments scrambled for clarification of the rules, which appeared vague and open to interpretation, a top Chinese policy maker on matters related to the South China Sea tried to calm worries inspired by the announcement.
Wu Shicun, the director general of the foreign affairs office of Hainan Province, said Saturday that Chinese ships would be allowed to search and repel foreign ships only if they were engaged in illegal activities (though these were not defined) and only if the ships were within the 12-nautical-mile zone surrounding islands that China claims.
The laws, passed by the provincial legislature, come less than a month after China named its new leader, Xi Jinping, and as the country remains embroiled in a serious dispute with Japan in the East China Sea over islands known in China as the Diaoyu and as the Senkaku in Japan.
The laws appear to have little to do with Mr. Xi directly, but they reinforce fears that China, now the owner of an aircraft carrier and a growing navy, is plowing ahead with plans to enforce its claims that it has sovereign rights over much of the sea, which includes dozens of islands that other countries say are theirs. And top Chinese officials have not yet clarified their intent, leaving room for speculation.
If China were to enforce these new rules fully beyond the 12-nautical-mile zones, naval experts say, at stake would be freedom of navigation, a principle that benefits not only the United States and other Western powers but also China, a big importer of Middle East oil.
An incomplete list of the laws passed in Hainan was announced by the state-run news agency, Xinhua, last week.
In an interview here Saturday, Mr. Wu said the new regulations applied to all of the hundreds of islands scattered across the sea, and their surrounding waters. That includes islands claimed by several other countries, including Vietnam and the Philippines.
“It covers all the land features inside the nine-dash line and adjacent waters,” Mr. Wu said. The nine-dash line refers to a map that China drew up in the late 1940s that demarcates its territorial claims — about 80 percent of the South China Sea, whose seabed is believed to be rich in oil and natural gas.
That map forms the basis for China’s current claims. Some neighboring countries were outraged when China recently placed the nine-dash map on its new passports. Vietnam has refused to place its visa stamps in the passports as they are, insisting a separate piece of paper be added for the stamp.
Mr. Wu, who also heads a government-sponsored institute devoted to the study of the South China Sea, said the immediate intention of the new laws was to deal with what he called illegal Vietnamese fishing vessels that operate in the waters around Yongxing Island, where China recently established an expanded army garrison.
The island, which has a long airstrip, is part of a group known internationally as the Paracels that is also claimed by Vietnam. China is using Yongxing Island as a kind of forward presence in a bid for more control of the South China Sea, neighboring countries say.
The Chinese Foreign Ministry said last week that China was within its rights to allow the coast guard to board vessels in the South China Sea.
The new rules go into effect on Jan. 1. According to a report in an English-language state-run newspaper, China Daily, the police and coast guard will be allowed to board and seize control of foreign ships that “illegally enter” Chinese waters and order them to change course.
Mr. Wu acknowledged that the new rules had aroused alarm in Asia, and the United States, because they could be interpreted as a power grab by China.
“A big worry for neighboring countries and countries outside the region is that China is growing so rapidly, and they see it is possible China taking over the islands by force,” he said. “I think China needs to convince neighboring countries that this is not the case.” Essentially, he said, countries had to trust that China would not use force in the sea.
The Philippines, an ally of the United States and one of the most vociferous critics of China’s claims in the South China Sea, reacted strongly to the new rules.
