The reclusive country is believed to have started work on an unknown vessel due to activity at the shipyard.
The latest images taken of the shipyard show that two heavy-lift barge cranes are working on a submerged object just off the main construction hall’s launching ramp.
While the nature of the object is unclear, what is visible suggests a sunk mother ship or small submarine.
The shipyard is where the communist country worked on its SINPO-class experimental ballistic missile submarine (SSBA) which now appears to have been moved, indicating that whatever work was being carried out is now complete.
A report by 38 North concludes that due to the activity detected at the site, a shipbuilding programme is underway.
It also indicated that there no activities suggesting either previous or forthcoming ejection tests at the facility’s test stand
The report says: “During this year, the rail-mounted tower and gantry cranes at the construction hall’s parts storage yards continue to be re-positioned, as is the case with the rail-mounted transfer table that is visible in the present image.
“Additionally, the contents of the storage yards have continued to change.
“All this activity suggests an ongoing shipbuilding programme of some type.
“While the Sinpo South Shipyard has historically been involved in the construction or repair of submarines, infiltration mother ships, small combatants and hovercraft, it is not apparent what type of shipbuilding program is being pursued.”
It continues: “Two heavy-lift barge cranes are working on a submerged object just off the main construction hall’s launching ramp.
“While the nature of the object is unclear, what is visible suggests a sunk mother ship or small submarine.”
The report comes as tensions continue to between the North Korean’s dictator Kim Jong-un and US President Donald Trump.
Along with a war of words and name-calling between the two leaders, Mr Trump put on a show of military might yesterday, sending six military aircraft, including two supersonic bombers to the Korean peninsula.
A number of countries, including the US, UK and South Korea issued a warning to North Korea earlier today.
A total of 11 countries said that they would hold a joint military drill on the peninsula.