The nuclear-armed North had "fired an unidentified projectile into the East Sea", Seoul's joint chiefs of staff said in a statement to AFP.

No further details were immediately available, including the device type, how far it travelled, and whether more than one projectile was involved.

It came days after the North's official Korean Central News Agency reported that it had test-fired a new "long-range cruise missile" over the weekend, calling it a "strategic weapon of great significance".

Pictures in the Rodong Sinmun newspaper on Monday showed a missile exiting one of five tubes on a launch vehicle in a ball of flame, and a missile in horizontal flight.

Such a weapon would represent a marked advance in North Korea's weapons technology, analysts said, better able to avoid defence systems to deliver a warhead across the South or Japan -- both of them US allies.

The missiles fired at the weekend travelled 1,500-kilometres (about 930 miles), on two-hour flight paths -- including figure-of-eight patterns -- above North Korea and its territorial waters to hit their targets, according to KCNA.

North Korea is under international sanctions for its nuclear weapons and ballistic missile programmes, which it says it needs to defend itself against a US invasion.

But Pyongyang is not banned from developing cruise missiles, which it has tested previously.