North Korea fired a salvo of short-range ballistic missiles early on Wednesday, Seoul's military said, Pyongyang's second such weapons test in a week.

Seoul's Joint Chiefs of Staff said it had "detected and (was) analysing several short-range ballistic missiles launched to the northeast around 06:50 (2150 GMT)".

"In preparation for additional launches, our military has strengthened monitoring and vigilance, while closely sharing information," with allies Tokyo and Washington, it added.

Japan also confirmed the launch, with the country's coastguard saying one missile had splashed down already.

"Vessels please pay attention to information coming ahead and if you spot fallen objects please don't approach closer but report it to the coastguard," it said in a statement.

Last Thursday, North Korea fired what Seoul described as multiple short range ballistic missiles into waters east of the Korean peninsula, the nuclear-armed country's first major weapons test since early July.

North Korean state media later claimed that this had been a test of a "new-type 600mm multiple rocket launcher". (AFP)