China's foreign ministry says it has launched an investigation into reports that a group of North Koreans seized three Chinese fishing vessels and took their 29 crew members hostage.

The ministry said on Wednesday that it is trying to obtain confirmation about the incident from North Korean authorities.

Chinese media reported that the seizures occurred near the city of Dalian, in Dandong province, on May 8.

The North Korean captors have reportedly forced the abducted fishermen to call their families and asked them to pay ransoms in order for them to be released.

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According to media reports, one fisherman, who narrowly escaped from being kidnapped, reported the abductions to local maritime police in Dalian following his getaway.

On the morning of last Wednesday, an abducted crew member apparently made a phone call using an unidentifiable number, claiming that the captors were requesting ransom amounts in return for the release of the fishermen.

Discussing the significance of the incident, which could potentially harm North Korea's relations with its chief ally, Al Jazeera's Melissa Chan said: The relationship between China and North Korea has been difficult over the past month since last month's attempted rocket launch.

"This could be a message from the North Koreans to [the Chinese to] back off. It could have been sanctioned by Kim Jong-un, the new supreme leader.

"The Chinese are very upset at North Korean behaviour over the rocket-launch bid and the possibility that there will be nuclear tests.

"The Chinese have been putting a lot of pressure on the North Koreans and the latter have not been taking it very well."

Source: Al Jazeera and agencies