South Korea successfully test-fired a submarine-launched ballistic missile (SLBM) on September 15, becoming only the seventh country in the world with the advanced technology and raising the prospect of a regional arms race.

The test, supervised by President Moon Jae-in, came hours after nuclear-armed North Korea fired “two short-range ballistic missiles” from South Pyongan province into the sea off its east coast, according to Seoul’s Joint Chiefs of Staff, and as China’s foreign minister visited Seoul.

Flying about 800km at a maximum altitude of around 60km, it was Pyongyang’s second firing in less than a week, after its official Korean Central News Agency reported it had test-fired a new “long-range cruise missile” over the weekend.

“It’s extraordinary timing that you have not one but two Koreas testing ballistic missiles on the same day,” Yonsei University professor John Delury told AFP. “It does speak to the fact that there’s an arms race in this region that everyone needs to pay attention to.”

The South’s missile was fired underwater from its newly commissioned Dosan Ahn Chang-ho-class submarine, and flew the planned distance before hitting its target, the presidential Blue House said.

All other countries with proven SLBM capabilities have nuclear weapons of their own.

It is a strategic advance for the South, which has been strengthening its military capabilities as it seeks to counter the threat posed by the North, which is under international sanctions for its nuclear weapons and ballistic missile programmes.

With the successful tests, South Korea now has “sufficient deterrence to respond to North Korea’s provocations at any time”, President Moon said, urging the South to continue increasing its weapons programmes to “overwhelm North Korea’s asymmetric power”.