"Some workers are pulling out of the site," an unidentified South Korean government insider informed the news agency.
Pyongyang is anticipated to next fit its Unha 3 rocket with radar and other supplementary systems and then move to fueling. North Korea has announced a launch window of Dec. 10 to 22.
"If the North begins fueling the rocket, fuel tanks will be seen around the launch site," the source said. "If many fuel tanks are spotted, we should take that as meaning that fueling has begun."
International monitoring of Dongchang-ri relies on commercial and military surveillance satellites as North Korea tightly guards its missile program.
IHS Jane's image specialist Allison Puccioni said "I don't believe that a launch is imminently imminent, but what we are seeing is sort of what they call the beginning of the end of launch preparations," CNN reported. "Prior to this, we had not seen much in the way of rocket launchpad activity, but now we are seeing some significant stuff happening."
That includes heightened activity on the rocket firing tower, according to the analyst.
Puccioni said there is a good likelihood North Korea will meet its stated launch timeframe. "I would not be surprised ... if it is within the window," particularly given the most recent pictures that reveal more work on the launchpad, she said.
The United States and its allies in the region have said the rocket launch would breach U.N. Security Council resolutions prohibiting North Korean ballistic missile operations.
Secretary of State Hillary Clinton on Tuesday called for NATO and Russia to add their voices in condemning the coming space launch, which is seen as a cover for another long-range missile test, Agence France-Presse reported. The North's most recent attempt failed in April when the rocket broke apart within minutes of takeoff.
"We urge everyone here to publicly call upon North Korea to comply fully with its U.N. Security Council obligations," Clinton said at a gathering of the NATO-Russia Council in Belgium.
The Security Council will carry out "appropriate steps" should Pyongyang go through with its rocket firing, Kyodo News quoted the body's December chairman, Moroccan Ambassador Mohammed Loulichki, as telling journalists on Tuesday.
South Korean Foreign Minister Kim Sung-hwan on Wednesday said the North would be penalized for proceeding with the launch, Yonhap reported.
"We and our neighbors will continue to persuade North Korea to drop the planned launch to the end, but if the North pushes ahead with the launch, it will have to some degree pay a price," the minister said.