The Philippines government has detained 11 Chinese fishermen and their boat in the South China Sea, prompting an angry response from Beijing.
The incident threatens to worsen relations between Beijing and Manila, which are involved in a bitter territorial dispute in the South China Sea.
Philippines maritime officials say the Chinese crew was apprehended early Tuesday close to the Half Moon Shoal in the Spratly Islands.
The men were found to be in possession of hundreds of sea turtles, some species of which are protected under Philippine wildlife protection laws.
Philippine officials say the fishermen are being brought to a nearby island, where they will be charged, possibly with poaching or other violations.
China's foreign ministry urged Manila to "immediately" free the fishermen. Spokeswoman Hua Chunying also demanded an explanation for what she called a "provocative" action.
"China has indisputable sovereign rights over the Spratly Islands, including the Half Moon Shoal, and their surrounding waters. A Chinese maritime police boat has arrived at the area. The Chinese foreign ministry and the Chinese Embassy in the Philippines have already lodged representations with the Philippine side, demanding that the Philippines make rational explanations and immediately release the detained fishermen as well as the boat. We warn the Philippine side against more provocative action."
Earlier, Chinese state media reported the fishermen missing after they were taken by "armed men" who boarded the boat by force.
The reports said those who boarded the boat fired five or six warning shots into the air. A Philippine official later told the New York Times no shots were believed to be fired.
Small-scale clashes involving fishing and other vessels occasionally break out in the South China Sea, where Beijing has overlapping claims with Vietnam, the Philippines, Taiwan, Malaysia and Brunei.
In 2012, China and the Philippines were engaged in a tense standoff over the Scarborough Shoal. Manila eventually withdrew its ships, but took the dispute to the United Nations International Tribunal on the Law of the Sea.
This angered Beijing, which prefers to solve the maritime disputes with one-on-one discussions and not international arbitration or multilateral forums. The arbitration case, which China has rejected, is expected to take years to complete.