Low level activity has been observed via satellite imagery at the Punggye-ri Nuclear Test Site, according to think tank 38 North which monitors the secretive state.
And camouflage paint has been added to the roofs of the Command Centre buildings near the North Portal, where test preparations have been spotted in recent weeks.
However little activity has been sighted at the portal itself, although it appears water is still being pumped out of it.
It is believed the move to camouflage the base may be an attempt to reduce the ability of foreign forces to observe and monitor activities at the site from overhead.
And it might also prevent some key buildings from being easily recognised, if the US or allied troops chose to go ahead with an attack.
This type of activity has been used at the nuclear test site before, most notably at the Main Administrative Area buildings in 2011.
A statement from 38 North said: “While it is perhaps too soon to determine the extent to which North Korea has, or will, change its historical pattern of activity at the test site, the renewed effort to employ disruptive pattern camouflage for passive defence at the Command Center at least suggests that North Korea is responding to a heightened sensitivity to overhead observation and monitoring and is attempting to make that more difficult (if not just to provide a new distraction).
“As before, on the basis of the analysis of satellite imagery alone, it is unclear if such activity indicates that a nuclear test has been cancelled, the facility is in stand-by mode, or that a test is imminent.”
The pictures come just days after similar satellite images revealed the hermit state has a second submarine missile launcher site.
The site was discovered at the Nampo Naval Shipyard on North Korea’s west coast, and could indicate Kim Jong-un has stepped up his submarine-launched ballistic missile (SLBM) programme.
And last month chilling images revealed “unusually high levels of activity” at Kim Jong-un’s Punggye-ri Nuclear Test Site.
Experts say the images could mean a nuclear test is “imminent” as US Secretary of State Rex Tillerson calls for North Korea to destroy its nuclear arsenal.
North Korea has already conducted five declared and remotely detected underground nuclear tests at its dedicated nuclear test site at Punggye-ri in mountainous terrain in the northeast of the country over the last decade.