A file photo shows Vietnamese fishing boat in the East Sea, known internationally as the South China Sea.
The United States said on Thursday that new Chinese fishing restrictions in disputed waters in the South China Sea were "provocative and potentially dangerous", as disquiet grew in Southeast Asia over the rules.
The legislature of China's Hainan province approved rules in November that took effect on Jan. 1 requiring foreign fishing vessels to obtain approval to enter waters under its jurisdiction.
Such a move, if broadly enforced, could worsen tensions in the region. Beijing claims almost the entire oil- and gas-rich South China Sea, known in Vietnam as the East Sea, rejecting rival claims to parts of it from the Philippines, Taiwan, Malaysia, Brunei and Vietnam.
The fishing rules add another irritant to Sino-U.S. ties, after China's recent announcement of an air defense identification zone in the East China Sea drew sharp criticism from Washington.
"The passing of these restrictions on other countries' fishing activities in disputed portions of the South China Sea is a provocative and potentially dangerous act," State Department spokeswoman Jen Psaki told a news briefing.
"China has not offered any explanation or basis under international law for these extensive maritime claims."
"Our long-standing position has been that all concerned parties should avoid any unilateral action that raises tensions and undermines the prospects for a diplomatic or other peaceful resolution of differences."
Fishermen from Vietnam and the Philippines have been caught up in heated territorial disputes with China on the seas in recent years. Last year, Vietnam accused China of opening fire on a fishing boat in the South China Sea, and later of endangering the lives of fishermen after ramming a fishing trawler.
China created the air defense zone in late November in an area that includes islands at the heart of a bitter territorial dispute with Japan.
The United States responded to that declaration by sending two B-52 bombers into the area without informing China. At the same time, it advised U.S. commercial carriers to operate in line with so-called notices to aviators issued by foreign countries.
The State Department spokeswoman gave no indication of any possible U.S. response to the fishing zone.
HAINAN HOME TO BIG NAVAL BASE
According to the website of the Hainan legislature, foreign fishing vessels need approval to enter from the "relevant and responsible department" of the Chinese government's Cabinet.
Hainan is responsible for administering the country's extensive claims to the myriad islets and atolls in the South China Sea.
It says it governs 2 million square km (770,000 square miles) of water, according to local government data issued in 2011. The South China Sea is an estimated 3.5 million square km (1.4 million square miles) in size.
The province is also home to Chinese naval facilities that include a purpose-built dock for the country's only aircraft carrier as well as a base for attack submarines.
The fishing rules do not outline penalties, but the requirements are similar to a 2004 national law that says boats entering Chinese territory without permission can have their catch and fishing equipment seized and face fines of up to 500,000 yuan ($82,600).
Vietnam reiterated its claim to sovereignty over the Paracel and Spratlys islands in the South China Sea, both also claimed by Beijing.
"All foreign activities at these areas without Vietnam's acceptance are illegal and groundless," Foreign Ministry spokesman Luong Thanh Nghi said in a written response to questions about the new fishing rules.
A government-affiliated fishing organisation, the Vietnam Fisheries Society, condemned the Hainan regulations.
"This action from China will directly affect Vietnamese fishermen, damage their work, their livelihoods and impact their families," said Vo Van Trac, vice chairman of the body.
Philippine Foreign Affairs Department spokesman Raul Hernandez said Manila had asked its embassy in Beijing to get more information on the rules.
Hainan officials were not immediately available to comment, but Foreign Ministry spokeswoman Hua Chunying said regulating the use of China's marine resources was a normal practice.