Chinese authorities were Sunday investigating claims that unidentified North Koreans hijacked a Chinese fishing boat, kidnapping 16 sailors and demanding a ransom, local media and an official said.

Armed North Koreans on May 6 hijacked the boat and escorted it towards North Korea while it was sailing in waters around 70 kilometres (40 miles) from North Korea's western coast, reports and the boat's owner Yu Xuejun said.

"The crew were taken away by a North Korean patrol boat after an armed hijacking," Yu told AFP, adding that the kidnappers had contacted him to demand a ransom of 600,000 yuan ($98,000).

"We are currently investigating (the boat owner's claims)," a section chief for the state border detachment, which is responsible for border security, in northeastern port city of Dalian, surnamed Zhao, told AFP.

The Southern Metropolis Daily said the Chinese embassy in North Korea told Yu it was "dealing with the matter".

Yu was not certain of the kidnappers' identity, but told AFP he suspected they were associated with North Korea's army.

Yu claimed to have been in contact with the 16 crew members as recently as Saturday, and said he believed they were in good health, but added that he was "worried that the North Koreans could abuse our sailors".

He had reported the incident to Chinese authorities, he said, but later posted details of the hijacking on the Internet out of frustration over an apparent lack of official action.

"It has almost been two weeks, but I haven't seen any results," he said.

The reported incident comes a year after the return of 29 fishermen also kidnapped by unidentified North Koreans who had demanded a 1.2 million yuan ransom.

The fishermen were returned without ransom after the foreign ministry said it had contacted North Korea in an effort to resolve the case, the state-run Xinhua news agency reported.

Tensions between North Korea and China, seen as its sole major ally, have been high in recent months after North Korea carried out a nuclear test in February, a move Beijing said it "firmly opposed".

The Global Times newspaper last year quoted Dalian residents as saying North Korean coastguards had in the past captured fishing boats and stolen fuel and other items on board.

Declining fishing stocks in often heavily polluted coastal waters have pushed Chinese fishermen further afield in recent years, prompting disputes with neighbouring countries.

Calls to Dalian's city government, and the local maritime safety bureau went unanswered on Sunday.