Airlines have re-routed flights as North Korea prepares to go ahead with its proposed long-range rocket launch.
The launch of the Unha-3 rocket, which North Korea says will merely put a weather satellite into space, breaches UN sanctions imposed to prevent Pyongyang from developing a missile that could carry a nuclear warhead.
Airlines, including South Korea's Korean Air Lines, Philippine Airlines and Cebu Air, have re-routed flights to avoid the rocket's path.
Russia, a former backer of North Korea which has boosted economic ties with Pyongyang, denounced the launch.
"We consider Pyongyang's decision to conduct a launch of a satellite an example of disregard for UN Security Council decisions," state-run news agency RIA quoted Russian Foreign Ministry spokesman Alexander Lukashevich as saying.
North Korea defended the launch as a sovereign right.
"The weight of our satellite is 100 kg. If it was a weapon, a 100 kg payload wouldn't have much of an effect... Our launching tower is built on an open site," said Ryu Kum-chol, vice director of the space development department of the Korean Central Space Committee.
Ryu said that the rocket assembly would be complete on Tuesday.
The launch is set to take place between Thursday and next Monday around the 100th birthday celebrations of the founder of North Korea, Kim Il-sung, whose grandson, Kim Jong-un, now rules. Kim Il-sung died in 1994.
"The launch of the Kwangmyongsong-3 satellite is the gift from our people to our great leader, comrade Kim Il-sung, on the occasion of his 100th birthday, so this cannot be a missile test," Ryu added.
The rocket will bisect a sea that separates South Korea and China and its flight path will take it towards the Philippines where a second stage of the rocket is due to come down in waters close to the archipelago.
China, which backs North Korea economically and diplomatically, reiterated its pleas for calm and said it had "repeatedly expressed its concern and anxiety about the developments", Foreign Ministry spokesman Liu Weimin told a press briefing in Beijing.
The prospect of a North Korean rocket launch has alarmed Japan, which was overflown by an earlier rocket and said it would shoot it down if it crossed its airspace.