South Korean authorities have warned Seoul would give a "merciless" response if its rival North Korea presses ahead with further provocations following the latest missile launch from a submarine.

Subsequent to Pyongyang's test-firing of submarine-launched ballistic missile (SLBM), the South has expressed serious concerns over the deteriorating situation in the Korean Peninsula.

In an emergency meeting convened after the missile launch, South Korean defence minister Han Min-koo said: "Retribution for provocations is an order from the people. Our military will stand with solid military readiness and make flat-out efforts for citizens to live their everyday lives at ease."

However, later in a press conference, Seoul authorities toned down their language in condemning the North.

"We judge North Korea's test-firing of a ballistic missile underwater last week to be very serious and worrying. We urge North Korea to immediately cease the development of SLBMs that undermine security on the Korean Peninsula and in Northeast Asia," defense ministry spokesman Kim Min-seok told reporters.

Experts have however played down North's capabilities in coming up with a fully-fledged SLBM saying they are out of Pyongyang's reach as yet. They say the missile has cruised only about 100 to 150 metres from the water surface.

"The North should first have the skills to produce miniaturized submarine-launched ballistic missile warheads. The North has conducted similar underwater test-fires several times in the past and last week's launch was made public for the first time, with its leader in attendance," a high-ranking military official was cited as saying by the Seoul-based Korea Times.

North Korea had earlier trumpeted about the "world-level strategic weapon" in unveiling the missile. The event, was overseen by North Korean leader Kim Jong-un and publicised along with several pictures by the state-run mouthpiece Korean Central News Agency.