China said the Philippines had to release the boat and the fishermen.
"China's Foreign Ministry and China's ambassador to the Philippines have made representations to the Philippines side, demanding that it provide a rational explanation and immediately release the people and the vessel", ministry spokeswoman Hua said.
"We once again warn the Philippines not to take any provocative actions," she said, adding that China had "indisputable sovereignty" over the Spratly Islands.
There are frequent tensions in the South China Sea between China and the other claimant nations, particularly Vietnam and the Philippines, both of which say Beijing has harassed their ships in the waters there.
While there are frequent stand-offs between fishermen and the various claimant states in the South China Sea, the actual detention of Chinese fishermen or the seizure of a boat is rare.
Not commercially driven
An oil industry official in China said the deployment of the rig owned by China's CNOOC oil company to waters near Vietnam appeared to be a political decision rather than a commercial one.
"This reflected the will of the central government and is also related to the U.S. strategy on Asia," said the official, who spoke on condition of anonymity because of the sensitivity of the issue.
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"It is not commercially driven. It is also not like CNOOC has set a big exploration blueprint for the region."
However, Wu Shicun, president of the National Institute for South China Sea Studies, a government think-tank in the southern province of Hainan, said China was unlikely to pay much heed to Vietnamese concerns.
"If we stop our work there as soon as Vietnam shouts, China will not be able to achieve anything in the South China Sea," Wu said.
"We have lost a precious opportunity to drill for oil and gas in the Spratlys. Also this time we are drilling in Xisha (Paracel Islands), not Nansha (Spratlys), there is no territorial dispute there. I think China will keep moving ahead with its plan (in Xisha), no matter what Vietnam says and does."
Tran Duy Hai, the Vietnamese foreign ministry official, raised the possibility of Hanoi taking the dispute to international arbitration.
"We cannot exclude any measures, including international legal action, as long as it is peaceful.
"We are a peace-loving nation that has experienced many wars," he said. "If this situation goes too far, we will use all measures in line with international law to protect our territory. We have limitations, but we will stand up to any Chinese aggression."
The Philippines has already taken its dispute with China to an international arbitration tribunal in The Hague.