North Korean leader Kim Jong-un oversaw the tests (Picture: AP)

North Korea has tested a new underwater nuclear weapon system, the state Korean Central News Agency (KCNA) said.

On Friday local time, the nation carried out the tests under leader Kim Jong-un’s guidance.

Cruise missiles were also shot during the weapon test and firing drill that took place from Tuesday to Thursday.

It comes just more than a week after the state agency said North Korea fired two strategic cruise missiles from a submarine earlier this month.

‘Strategic’ tends to be used for weapons that have nuclear capability, with the KCNA saying the tests show the missiles are reliable.

The submarine units form part of North Korea’s sprawling nuclear deterrents that have sent South Korean and Western intelligence agencies scrambling to analyse the specifics of.

Kim Jong-un oversaw the tests.