The fishermen and boats were seized March 4 and held at the Xisha Islands in the South China Sea, over which the countries had fought a decisive battle in January 1974, with China emerging victorious.
The area has remained a sore spot with Vietnamese fishers.
A statement from the South China Sea Fishery Bureau, under the Ministry of Agriculture, said after the detainees were released Friday they signed a written document stating they would not infringe on China's maritime and fishing rights in its territorial waters, the official Chinese news agency, Xinhua reported.
China alleged when a patrol boat seized the fishing vessels they contained 55 pounds of explosives along with tools used for dynamite fishing, Xinhua said.
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