Voice of America(VOA) said Saturday that around half of North Korean cargo ships traveling overseas are confirmed to be outdated models built more than 30 years ago.

The U.S. broadcaster cited data by the Port State Control in the Asia-Pacific, an agency overseeing vessels in the region. The data showed that 63 out of 129 North Korean ships inspected last year were over 30 years of age.

While noting that safety problems of a ship are directly linked to a vessel's old age, VOA said defects were found in all ships inspected and 25 were told to stop operating.

According to Japanese media, a North Korean vessel, the "Chong Gen," sunk in waters some 60 kilometers southwest of Fukue Island in Nagasaki Prefecture in the East Sea on Wednesday. The Japanese Coast Guard rescued all 26 sailors on board the boat, which was found be in its 27th year in service.

In South Korea, a ship's lifespan is set no longer than 30 years. In Japan, it's set much shorter at 18 years.