The rusting, 2,035-tonne general cargo vessel Kang Nam I was suspected of breaching 25 regulations after entering Hong Kong on Sunday.
London-based shipping publication Lloyd's List said the ship was being held under the terms of local shipping regulations, rather than those of UN sanctions imposed on North Korea after it conducted its first atom bomb test on October 9.
The government's Customs and Marine Departments would make no comment when contacted.
Lloyd's cited acting assistant director at the Marine Department, Lee Kai-leung, as saying that 12 safety concerns were "detainable deficiencies mainly on life-saving and fire fighting appliances as well as navigational equipment including out-dated and obsolete charts".
Hong Kong's English-language daily the South China Morning Post reported that the 22-man vessel was not carrying any cargo when it arrived and had come to load up with scrap metal.
The newspaper cited Hong Kong's marine chief Roger Tupper as confirming the detention.
Tupper was quoted as telling the Post that eight other North Korean ships had been similarly stopped this year.
"Hong Kong is a major hub port and North Korean vessels do sometimes visit," he said. "It is not unreasonable that they are subject to routine Port State Control inspections."
The reports said the ship had arrived from Shanghai and was due to return home to Nampo, near Pyongyang, via Taiwan.
They said the captain, who would not give his name, had told reporters he was unaware of Pyongyang's first ever atom bomb test, nor of the subsequent UN sanctions.
The clampdown was put in place to prevent the hard-line Stalinist regime of Kim Jong-il from transferring or importing nuclear technology and to end the trade in contraband, such as drugs and illicit cigarettes, that is believed to help fund the North's nuclear programme.
The sanctions are part of a huge global diplomatic effort since the test to persuade North Korea to abandon its nuclear weapons programme.

Copyright AFP (Agence France-Presse), 2006