Asian airlines said they will divert planes from the intended flight path of North Korea's rocket as shipping in the area was warned Tuesday to beware of falling debris.

Japan's two largest carriers, Japan Airlines and All Nippon Airways said they will alter the route of flights between Tokyo and Southeast Asian cities including Manila, Jakarta and Singapore during the planned rocket launch window.

Philippine Airlines said it "plans to reroute some of its flights in view of the possible effects on a portion of Philippine territory of the satellite launch of North Korea within the month."

The moves came as Philippine air control authorities declared a no fly zone in airspace where North Korea's rocket was projected to pass, a Japanese transport ministry official told AFP.

"The Japanese side are also preparing to issue a 'notice to airmen' that warns them not to enter a no fly zone set by the Philippine authorities," he said.

"These no fly zone-related notices should apply to all international carriers," he added.

The re-routing comes as North Korea ramps up its preparations for what it says is a peaceful satellite launch, but what Japan and its Western allies claim is a disguised missile test.

Pyongyang insists the launch, which is planned for some time between April 12 and 16 to mark the centenary of the birth of late founding president Kim Il-Sung, is its right.

But countries around the globe have condemned the plan, which they say will contravene UN resolutions.

South Korea has vowed to shoot down the rocket if it strays into its territory. Japan has said it may do likewise.

The South's military plans to deploy destroyers armed with missiles to the Yellow Sea to track the rocket.

The transport ministry in Seoul said it would provide up-to-date information to shipping on the rocket launch.

All 15 maritime traffic control centres will be placed on alert from Wednesday, issuing navigation warnings every two hours to protect vessels operating in the Yellow Sea, it said.

The first stage of the rocket is expected to fall in waters 170 kilometres (100 miles) west of Gunsan in the southwest of South Korea, it said.

Japan's coast guard on Tuesday began issuing warnings to ships in the area to be on the lookout for falling debris from the rocket.

"We are announcing by radio the expected time and places where falling objects could appear," coast guard spokesman Yoshiyuki Terakado said.

Coast guard officials will issue the warning every day in Japanese and English until the launch is confirmed, he said.

In the Philippines, commercial fishing vessels have been told to remain in port during the launch window.

Office of Civil Defence chief Benito Ramos said evacuation plans had also been put in place in case debris fell on the Philippines' island of Luzon.

"Our concern is that in a worst case scenario the trajectory (of the rocket) deviates by even a few degrees, it could jettison its booster over mainland Luzon and there could be a lot of people affected," he said.

The Philippine navy has deployed ships northeast of Luzon.

Vice Admiral Alexander Pama said: "I don't think there is anyone who can exactly say where the rocket (debris) will land, so we are working in the context of estimates. Our naval forces have already been given heads up to be on alert."

"As we speak now, plans are being put in place relative to contingencies that could happen. The ships are going to be there in case there is a need for assistance just in case vessels get hit," he said.