"North Korea fired an unknown projectile from the Sunan area around 09:30 today, but it is presumed that it failed immediately after launch," Seoul's Joint Chiefs of Staff said in a statement.

Japanese media reported that North Korea had launched a possible ballistic missile, citing an unnamed defence ministry official.

The failed launch would have been Pyongyang's tenth weapons test this year, following seven missile tests and two of what North Korea said were a "reconnaissance satellite".

South Korea and the US said last week those tests were actually of a new intercontinental ballistic missile (ICBM) system -- a so-called "monster missile" that has never been test-fired before.

North Korea is already under biting international sanctions over its missile and nuclear weapons programme but the US said the tests were a "serious escalation" and would be punished.