The new regulations, adopted by China's Hainan province and effective since Jan. 1, require foreigners and foreign fishing vessels to get approval from the central government to enter waters under its jurisdiction, China's state-run Xinhua News Agency reported.
China and other countries have been disputing who controls several island groups in the South China Sea. Also, China has laid claim to much of the South China Sea, raising international concerns.
U.S. State Department spokeswoman Jen Psaki Thursday said passage of the restrictions on other countries' fishing activities in disputed portions of the South China Sea "is a provocative and potentially dangerous act."
"These regulations appear to apply to the maritime space within China's so-called nine-dash line," Psaki said. "China has not offered any explanation or basis under international law for these extensive maritime claims."
The "nine-dash line" refers to the demarcation line used by the Chinese government in claiming part of the South China Sea that includes several disputed island groups.
During a Friday media briefing, Foreign Ministry spokeswoman Hua Chunying said, "For the last 30 years, China's relevant laws and regulations have been implemented normally, without causing any tension."
International and domestic laws give China the right to manage the biological and non-biological resources on relevant islands, reefs and waters, Hua said.
"If someone asserts that the technical amendments on a provincial fishing regulation, which has been implemented for years, will pose a threat to regional peace and stability, it's either due to lack of common sense or out of hidden intent," she said.
Psaki said the U.S. position has been that all parties should "avoid any unilateral action that raises tensions and undermines the prospects for a diplomatic or other peaceful resolution of differences. And clearly, passing legislation that claims ownership over territory in a disputed area would certainly be of concern to us, as I expressed."
Hua urged the United States to respect and support countries' efforts to settle problems by direct conversation and avoid sending the wrong message, Xinhua said.