"North Korea sent unknown ballistic missile towards East Sea," South Korea's military said.

Monday's launch took place while outgoing US Secretary of State Antony Blinken was visiting Seoul for talks with some of its key ministers.

The ballistic missile launch is Pyongyang's first this year and comes after its last in November when it test-fired what it said was its most advanced and powerful solid-fuel intercontinental ballistic missile (ICBM).

That was North Korean leader Kim Jong Un's first weapons test since being accused of sending soldiers to help Russia fight Ukraine.

In response, South Korea fired a ballistic missile into the sea in a show of force after Pyongyang's salvo of missile launches.

South Korea, a vibrant democracy, has also been plunged into weeks of crisis by its sitting president Yoon Suk Seol, who declared a short-lived martial law decree on December 3.

North Korean state media last week said the South was in "chaos" and paralysed politically over an attempt by investigators to execute an arrest warrant for Yoon.