North Korea has been injecting liquid fuel into the rocket it intends to send into space soon.
The West deems the launch provocative but Pyongyang claims it is a peaceful centrepiece to celebrations marking the 100th anniversary of the nation's founder.
The final preparations at the west coast launchpad were taking place as North Korea's ruling Workers' Party convened for a special conference.
Delegates are expected to further elevate new leader Kim Jong Un by giving him new titles, including some held by his father, the late Kim Jong Il.
The conference, being held at an undisclosed location in Pyongyang, is one of two major political gatherings this week that are expected to formally install the young Kim as North Korea's supreme leader.
Two days after the political conference, the Supreme People's Assembly will gather to ratify new legislation. The events come as North Korea celebrates the April 15 centennial of the birth of Kim Jong Un's grandfather, Kim Il Sung, a major milestone in the nation he founded in 1948.
North Korea has thrown open its doors to a select group of journalists and visitors from abroad for two weeks of celebrations in what might be the largest influx of foreigners in years. North Korea also marks the 80th anniversary of the founding of the Korean People's Army, another key event, on April 25.
Space officials call the launching of the Unha-3 rocket, mounted with an Earth observation satellite, the crowning glory in a week of events meant to celebrate Kim Il Sung's birthday.
The US, Japan, Britain and others, however, see it as a provocation and violation of UN Security Council resolutions banning North Korea from developing its nuclear and missile programmes. Experts say the Unha-3 carrier is similar to the type of rocket that could be used to fire a missile mounted with a nuclear warhead to strike the US or other targets.
Paek Chang Ho, chief of the North Korean space committee's General Command Centre, denied that the launch was anything but a peaceful, civilian bid to send a satellite into space. He said the satellite would send back images and data used for weather forecasts and agricultural surveys, adding: "We don't really care what the outside world thinks. This launch is critical to developing our space programme and improving our economy."