SEOUL (AFP) - North Korea has been repeatedly moving multiple missiles around in an apparent bid to confuse outside intelligence gatherers ahead of an expected launch, Yonhap reported on Thursday.

According to intelligence analysis cited by the South Korean news agency, two mid-range Musudan missiles have been repeatedly moved in and out of a warehouse facility on its east coast.

At the same time, at least five mobile launch vehicles have also been spotted swapping places and positions.

"There are signs the North could fire off Musudan missiles any time soon," an intelligence source told Yonhap.

"But the North has been repeatedly moving its missiles in and out of a shed, which needs close monitoring."

Another source suggested Pyongyang was hoping to "fatigue" South Korean and US intelligence gatherers who have been on a heightened state of surveillance alert since Wednesday.

The mid-range missiles mobilised by the North are reported to be untested Musudan models with an estimated range of anywhere up to 4,000km.

That would cover any target in South Korea and Japan, and possibly even US military bases on the Pacific island of Guam.

North Korea has proved quite adept at confounding intelligence monitoring in the past.

Its long-range rocket launch in December had been widely flagged in advance and was subjected to intense satellite scrutiny.

In the end, the rocket blasted off hours after a succession of South Korean media outlets, citing satellite imagery analysis by government, diplomatic and military sources, suggested the launch was facing a lengthy delay.

Yonhap news agency had quoted military officials as saying the entire three-stage Unha-3 carrier had been removed from the launch pad and returned to a nearby assembly facility for repair.

Various Japanese media on Thursday reported defence officials confirming that at least one of the North Korean mobile launchers had placed its pad in a launch-ready position.

The reports also said that such moves could be deliberate attempts by North Korea to sow confusion and did not necessarily indicate a launch was imminent.

A defence ministry spokesman contacted by AFP declined to comment, citing a desire not to compromise secrecy surrounding intelligence-gathering capabilities.

Japan's Chief Cabinet Secretary Yoshihide Suga, asked about the reports, said the government was doing everything it can "to protect the lives and the safety of our people".

"We are aware of all sorts of information. We are sharing information with South Korea and the United States," Mr Suga said.