North Korea's five-day window to launch a rocket that has deeply antagonised global opinion opened on Thursday with no immediate signs of takeoff being imminent.

The communist state has said it will launch the rocket between Thursday and Monday, most likely between 2200 GMT and 0300 GMT, to mark Sunday's centenary of the birth of its founding leader Kim Il-Sung.

The rocket will place a satellite in orbit for peaceful research purposes, North Korea says, but Western critics see the launch as a thinly veiled ballistic missile test. The United Nations has banned such tests by Pyongyang.

North Korea says it has installed the satellite payload and fuelled the 30-metre (100-foot) rocket, but officials in South Korea and Japan said there was no sign that liftoff was about to happen on Thursday morning.

"So we believe there is very little possibility of the rocket being launched today, as it said earlier the launch would take place between 7:00 am and noon," a South Korean government official told Yonhap news agency.

A spokesman for South Korea's defence ministry told reporters: "We're closely watching developments."

Japanese Prime Minister Yoshihiko Noda said his country was on full alert, while urging North Korea to show "self-restraint until the last minute".

"But we want to be fully prepared for any possible contingency," Noda said, after ordering the deployment of anti-missile batteries on land and at sea to shoot down the rocket if it threatens Japanese territory.

The Japanese government's top spokesman Osamu Fujimura told reporters in Tokyo that he had no fresh information about the planned launch.

Japan, Philippines on alert ahead of N. Korean launch
Tokyo (AFP) April 12, 2012 - Japanese Prime Minister Yoshihiko Noda said Thursday that the country was on full alert over North Korea's planned rocket launch, expected at any time over the coming days.

"We want to seek their self-restraint until the last minute," Noda told reporters as he arrived for talks with a special taskforce set up to handle Japan's response to the planned launch.

"But we want to be fully prepared for any possible contingency," Noda said.

Poor but nuclear-armed North Korea has said it plans to launch a satellite between Thursday and Monday to mark the centenary of the birth of late founding president Kim Il-Sung.

Western critics see the launch as a thinly veiled missile test banned by UN Security Council resolutions.

Tokyo has deployed missile defence systems to intercept and destroy the rocket if it looks set to fall on Japan, much as it did in 2009 before Pyongyang's last long-range rocket launch.

The Philippine government has ordered flights to divert to avoid being in the area where debris might fall, the head of air traffic control said.

From April 12 to 16, about 20 flights a day will be affected by the order, said Michael Mapanao, head of the aviation authority's air traffic control department.

"They will have to go around to clear the airspace. It will add additional minutes to their flying time," he said.

Philippines civil defence chief Benito Ramos has also ordered shipping to avoid the area where rocket debris is expected to fall, with the police, coast guard and navy all enforcing the ban.

"There are no more people in the exclusion zone," he said.

He brushed aside complaints that the government was overreacting to the rocket launch.

"It is better to be overreacting than not to be reacting when something happens," he told ABS-CBN television.

In Japan's Ishigaki island in the southern Okinawan archipelago, which lies right below the announced trajectory of the rocket, city officials went on standby at 6 am Thursday (2100 GMT Wednesday), an hour before the five-day launch window opened.

"We will continue this standby condition every day from 6am to 2pm until Monday," Ishigaki city official Choichi Ameku said, referring to the time of day North Korea is expected to schedule the launch.

Residents have been told to take shelter in buildings as soon as the rocket is launched and not to approach any debris that appears to have fallen from the rocket as it could be highly toxic, officials said.

The Japanese government has told residents to "carry on their normal daily lives" but to reschedule athletics events for school children from the morning to the afternoon, Ishigaki's education official Akira Sakiyama said.

"So far, residents are going about their business as usual," he added.