Senior military officers observed the tests conducted in the sea off the North's east coast, state media KCNA said. It said the test had no adverse impact on the security of neighbouring countries.
The tests were aimed at assessing the readiness of North Korea's underwater combat systems, improving the Navy's ability to carry out strategic missions and demonstrating the reliability of its nuclear deterrent, state media said.
North Korea has pushed ahead with modern missile submarines and both ballistic and cruise missile developments, test-launching them from various platforms including an ageing submarine.
Pyongyang is not yet believed to have launched a modern missile submarine in full operation. This is a top military priority of the country's leader Kim Jong-un, who has overseen the development of a range of strategic ballistic and cruise missiles.
South Korea's military did not immediately comment on the tests.
The launches extended a recent run in weapons demonstrations, including tests of various hypersonic missile systems on September 20 and October 3 that the North said were aimed at advancing its arsenal of weapons designed to overwhelm missile defences in South Korea and Japan.
North Korea in recent weeks has also conducted live-fire drills and commissioned a new warship as Kim continues to flaunt his nuclear weapons program while rejecting US and South Korean offers to resume long-stalled diplomacy.
Kim in recent years has halted all diplomacy and co-operation with South Korea and described it as a permanent enemy amid a stalemate in larger nuclear negotiations with Washington.
He has so far rebuffed US President Donald Trump's calls to revive their diplomacy, which broke down in 2019.
with AP
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