China has called on North Korea to release a private Chinese fishing boat and its crew, after the boat's owner reported the detention 10 days ago, state media says.

The owner of the boat took to a microblog this weekend to raise attention to the detention that happened on May 5.

Yu Xuejun said unidentified gun-wielding North Koreans took his boat and 16 crew members in what he said were Chinese waters and that the North Koreans wanted a 600,000 yuan ($100,000) ransom.

The diplomatic difficulty comes at a time of high Chinese frustrations with North Korea after it conducted a nuclear test and missile launches.

Yu called the Chinese Embassy for help on May 10 after the boat was "grabbed" by North Korea, the official Xinhua News Agency said late on Sunday, citing an official at the Chinese Embassy in Pyongyang, Jiang Yaxian.

The embassy promptly contacted the North Korean Foreign Ministry's Bureau of Consular Affairs, "asking [North Korea] to release the boat and the fishermen as soon as possible", said Jiang.

He said the embassy would "continue efforts to ensure that the issue will be properly addressed at an early date".

Ransom

Owner Yu said on a verified Tencent Weibo microblog late on Saturday that he was appealing for help from Internet users and the Foreign Ministry.

The Southern Metropolis Daily reported on Sunday that Yu received a call from North Korea saying his boat had entered North Korean waters. It quoted an unnamed official from Liaoning province's maritime police as confirming the case had been reported to them on May 6 and a team was handling it.

Yu said the North Korean side had asked for the ransom to be paid by noon on Sunday to a company in Dandong, a city in northeastern China on the North Korean border, or they would confiscate the boat and repatriate the crew.

In May last year, a North Korean boat hijacked three Chinese boats with 29 fishermen on board. State media said then that the unidentified captors demanded $190,000 for the fishermen's release. They were freed within two weeks.

China is North Korea's economic lifeline, providing nearly all of its fuel and most of its trade. North Korea's economic dependence on China is rising, following a standoff with South Korea that effectively shut an industrial park that was an important source of hard currency.