The launch of SLBM by North Korea is seen as a threat to regional peace and stability as the distance covered by the projectile has far exceeded any previous SLBM tests.
North Korea fired a submarine-launched missile on Wednesday that flew about 500 kilometres towards Japan. The missile landed in Japan's air defence identification zone (ADIZ) in the Sea of Japan.
The firing of submarine-launched ballistic missile (SLBM) is seen as a show of the improving technological capability of North Korea, which has conducted a series of launches in defiance of UN sanctions.
Having the ability to fire a missile from a submarine could help North Korea evade a new anti-missile system planned for South Korea. Weapon experts say that if North Korea's land-based arsenal is destroyed, the country would still be able to launch missiles from the sea.
Officials at South Korea's Joint Chiefs of Staff and the Defence Ministry confirmed that the ballistic missile was fired at around 5:30 am (2030 GMT) from near the coastal city of Sinpo where a submarine base is located.
The projectile reached Japan's air defence identification zone (ADIZ) for the first time, Chief Cabinet Secretary Yoshihide Suga told a briefing, referring to an area of control designated by countries to help maintain air security.
The flight distance, which was tracked by South Korea's military Joint Chiefs of Staff, far exceeded any previous SLBM tests, suggesting significant progress in technical prowess.
The missile was fired at a high angle, South Korea's Yonhap News Agency reported, an indication that its full range would be around 1,000 kilometres at an ordinary trajectory.
North Korea's "SLBM (submarine-launched ballistic missile) technology appears to have progressed," a South Korean military official told Reuters.
Director of the East Asia Non-proliferation Program at the Middlebury Institute of International Studies in California, Jeffrey Lewis, said the test appeared to be a success.
"We don't know the full range, but 500 kilometres is either full range or a full range on a lofted trajectory. Either way, that missile works."
"This system is still in development, but North Korea is clearly making progress," he said.
The launch came two days after rival South Korea and the United States began annual military exercises in the South, which North Korea has condemned as preparation for an invasion while threatening retaliation.
China opposes THAAD
Beijing is Pyongyang's main ally but has joined past UN Security Council resolutions against the North. It has been angered by what it views as provocative moves by the United States and South Korea, including their July decision to base the THAAD (Terminal High Altitude Area Defence) anti-missile system in South Korea.
China opposes North Korea's nuclear and missile programme as well as any words or deeds that cause tension on the Korean peninsula, its foreign minister, Wang Yi, said on Wednesday at a meeting with his Japanese and South Korean counterparts in Tokyo.
South Korea's Foreign Ministry condemned the launch and warned of more sanctions and isolation for its rival that "will only speed up its self-destruction."
"This poses a grave threat to Japan's security, and is an unforgivable act that damages regional peace and stability markedly," Japanese Prime Minister Shinzo Abe told reporters, adding that Japan had lodged a stern protest.
Joshua Pollack, editor of the US-based Non-proliferation Review, said claiming to have mastered SLBM technology is as much about prestige as a military breakthrough, a status enjoyed only by six countries including the United States, Russia and China.
"I think it's meant foremost as a demonstration of sheer technical capability and a demand for status and respect," Pollack said.
South Korea believes the North has a fleet of more than 70 limited-range submarines. Acquiring a fleet of submarines large and quiet enough and with a longer range would be a next step for the North, experts said.
"They keep conducting nuclear tests and SLBMs together which means they are showing they can arm SLBMs with miniaturised nuclear warheads," said Moon Keun-sik, a retired South Korean navy officer and an expert in submarine warfare.
China, Japan and South Koera condemn missile launch
The foreign ministers of China, Japan and South Korea criticised North Korea's latest submarine missile test on Wednesday during their annual talks that were held amid lingering frictions over territorial disputes and wartime history.
Japanese Foreign Minister Fumio Kishida, who chaired the meeting with China's Wang Yi and South Korea's Yun Byung-se, said that North Korea's missile launch "simply cannot be tolerated".
Kishida said Tokyo lodged a protest to the North over the missile, and urged his counterparts to step up cooperation as they face the latest development.
"I hope to coordinate closely in order for Japan, China and South Korea to lead the efforts of the international community," he said.
North Korea has become further isolated after a January nuclear test, its fourth, and the launch of a long-range rocket in February which brought tightened UN sanctions.
It has launched numerous missiles of various types this year, including one this month that landed in or near Japanese-controlled waters.
Tensions on the Korean peninsula were exacerbated by the recent defection of North Korea's deputy ambassador in London to South Korea, an embarrassing setback to North Korean leader Kim Jong Un.