South Korean and US intelligence officials detected missiles being transported away from North Korea's Missile Research and Development Facility at Sanum-dong in the northern part of the capital.
The South claimed they could be intermediate Hwwasong-12 or intercontinental ballistic (ICBM) Hwasong-14 missiles.
However, the report stated the facility is dedicated to producing ICBMs.
South Korean officials have voiced concerns that North Korea could conduct more provocative acts near the anniversary of the founding of its communist party on October 10, or possibly when China holds its Communist Party Congress on October 18.
A source from South Korea’s Defence Ministry said he could not confirm details of the report or whether there have been any unusual activities in the area mentioned.
The secretive state threatened, via local media, to “shoot down” Donald Trump’s fighter jets after the US Air Force flew past the Demilitarised Zone.
The flyover marked the farthest north of the Demilitarised Zone any US fighter or bomber aircraft have flown off North Korea’s coast in the 21st century, chief Pentagon spokesman Dana White said last week.
In its editorial, the state-run North Korean outlet claimed: "The US flying its B-1B Lancers strategic bomber squadron over international waters in the East Sea was an immensely dangerous and reckless act that intends to drive the situation on the Korean Peninsula to extremes and an anti-North Korea provocation cannot be overlooked.
"The US' bellicose, youthful bravado is rather fanning the will for retaliation among tens of millions of our soldiers and civilians.
"Our military has been highly motivated with a resolve to shoot down the US flights seeking to trespass in our territorial skies."
It follows grainy images of the Nampo Naval shipyard on the hermit kingdom’s west coast show Kim is continuing to work on his second barge so his navy can carry out underwater test missile launches.
The 68ft barge is identical to another seen at the Sinpo South shipyard on the east coast which has been involved in up to six test launches since 2014.
According to 38 North, which monitors North Korea, it could suggest the hermit state is expanding the submarine-launched ballistic missile and development programme to the west coast.
Experts believe the aerial images of the Punggye-ri Nuclear Test Facility also show a central ring that is used to support a missile launch tube during testing.
In further signs work is continuing on the second barge, images show it in the same location but the portal crane on the east side is now rotated over.