North Korea has fired what appeared to be multiple land-to-ship missiles off its east coast according to South Korea's military.
The launch came a day after South Korea postponed full deployment of a controversial US anti-missile system designed to deter a North Korean attack.
South Korea said it will hold off on installing remaining components of the US Terminal High Altitude Area Defense (THAAD) system that has angered North Korea's main ally, China, amid early signs of easing tensions between the two countries.
The missile launches come less than a week after the United Nations Security Council passed fresh sanctions on the reclusive state, which said it would continue to pursue its nuclear and weapons programme without delay.
The projectiles were launched this morning from the North Korean coastal city of Wonsan, South Korea's Office of Joint Chiefs of Staff said in a statement.
South Korean President Moon Jae-in has been briefed on the latest launch, the military said, declining to give further details.
The launch is the fourth missile test by the North since President Moon took office on 10 May pledging to engage in dialogue with Pyongyang.
Under leader Kim Jong-un, North Korea has been conducting such tests at an unprecedented pace in an effort to develop an intercontinental ballistic missile (ICBM) capable of hitting the mainland United States.
Compared to the different types of ballistic missiles Pyongyang has recently tested, the missiles launched today are considered to be more defensive in nature, designed to defend against threats such as enemy warships.
North Korea unveiled a number of new weapons at a massive military parade on 15 April to mark the birth anniversary of the state's founding leader and has since tested some of them.
China has called for all parties to exercise restraint and take action to stabilise the situation.
A Chinese foreign ministry spokeswoman said: "The UN Security Council resolution has clear rules on [North Korea's] use of ballistic missiles technologies. All sides should work together to de-escalate tensions and take active steps to stabilize the region."
US President Donald Trump has been pressing China to rein in North Korea, warning that all options, including a pre-emptive military strike, are on the table if Pyongyang persists with its nuclear and missile development.
Seoul, Tokyo and Washington were analysing the launches for further information, officials said.
Japan's navy and air force conducted military drills with two US aircraft carriers in the Sea of Japan last week, following similar joint US-South Korea exercises.
"North Korea likely wanted to show off its ability to precisely target a large warship, in relation to the joint military drills involving US aircraft carriers," said a spokesman for South Korea's Joint Chiefs of Staff.
"By testing different types of missiles, North Korea also appears to be aiming to secure the upper hand in relations with South Korea and the United States."
The isolated country, which has conducted dozens of missile tests and tested two nuclear bombs since the beginning of 2016 in defiance of UN Security Council resolutions, says the programme is necessary to counter US aggression.