North Korea has fired two ballistic missiles across its east coast, South Korea's military says, its first ballistic missile test in six months.
The tests, a breach of UN resolutions, came as South Korea and China held meetings in an effort to get the North to resume denuclearisation talks.
The launches show the North has continued to develop its weapons despite a severe economic crisis.
Hours later, the South tested its first submarine-launched ballistic missile.
The test of the missile known as SLBM was pre-planned and not in reaction to the North's latest launches. It makes South Korea the seventh country in the world with such technology.
President Moon Jae-in, who attended the test, said South Korea now had "sufficient deterrence to respond to North Korea's provocations at any time", urging the South to continue increasing its weapons programmes to "overwhelm North Korea's asymmetric power".
The tests by both Koreas highlighted an arms race on the peninsula, as negotiations with North Korea remain stalled. The US wants the country to give up its nuclear and missile programmes in exchange for sanctions relief, but the North has refused.
The short-range missiles the North fired on Wednesday flew around 800 km (500 miles) at a maximum altitude of 60km, and were launched from central inland areas of the country, South Korea's Joint Chiefs of Staff (JCS) said.
They flew east towards the Sea of Japan, also known as the East Sea, the JCS added, saying South Korea and the US were conducting analysis to determine which type of missile was used.
The US Indo-Pacific Command said the missiles did not pose an immediate threat to US personnel, territory, or allies, but that they highlighted the "destabilising impact of [North Korea's] illicit weapons programme".
Japanese Prime Minister Yoshihide Suga called the launch "outrageous", saying it threatened peace and security in the region.
Experts say Pyongyang carries out such tests to improve its technology while trying to increase its leverage in negotiations with Washington.
"It's extraordinary timing that you have not one but two Koreas testing ballistic missiles on the same day," Prof John Delury at Yonsei University told AFP news agency. "It does speak to the fact that there's an arms race in this region."
Earlier, China's Foreign Minister Wang Yi held talks with his South Korean counterpart, Chung Eui-yong, in Seoul, and said all parties should work to promote peace and stability on the Korean peninsula.
"Not only North Korea but other countries are carrying out military activity," he said. "All of us should make efforts in a way that helps resume dialogue."
UN resolutions ban North Korea from carrying out tests with ballistic missiles - which can carry either nuclear or conventional warhead - in efforts to curb the country's nuclear programme.
Ballistic missiles are classed according to how far they can travel, the furthest of which being an intercontinental ballistic missile (ICBM).
North Korea has in the past tested ICBMs said to be capable of reaching nearly all of western Europe and about half of the US mainland.
Last weekend, Pyongyang said it tested a long-range cruise missile capable of hitting much of Japan, calling it "a strategic weapon of great significance". Experts say it could possibly carry a nuclear warhead.
The UN Security Council does not forbid the test of cruise missiles. But it considers ballistic missiles to be more threatening because they can carry bigger and more powerful payloads, have a much longer range, and can travel faster.
North Korea is facing food shortages, and has spent more than a year in isolation. It cut off most trade with its closest ally China to stop the spread of Covid-19.
Last March, Pyongyang defied sanctions and tested ballistic missiles, which triggered a strong rebuke from the US, Japan and South Korea.
And last month the UN atomic agency said North Korea appeared to have restarted a reactor which could produce plutonium for nuclear weapons, calling it a "deeply troubling" development.
Source: BBC