"North Korea fired three short-range ballistic missiles toward the East Sea," the Joint Chiefs of Staff said in a statement, referring to the body of water also known as the Sea of Japan.

An air raid warning was issued for the island of Ulleungdo, JCS said, which was flashed on national television and told residents to "evacuate to the nearest underground shelter".

The military said one of Pyongyang's missiles had landed in international waters south of the Northern Limit Line, the disputed maritime border between the two countries.

South Korean President Yoon Suk-yeol called a meeting of the National Security Council over the launch, which analysts said was one of the most "aggressive and threatening" in many years.

Japan also confirmed the launch of suspected North Korean ballistic missiles, with the coastguard warning vessels to take care.

Japanese Prime Minister Fumio Kishida told reporters: "As we see tensions rising in the Korean Peninsula, I would like to hold a national security meeting as soon as possible."

Pyongyang's latest launch comes as Seoul and Washington stage their largest-ever joint air drills, dubbed "Vigilant Storm", which involve hundreds of warplanes from both sides.

Pak Jong Chon, a high-ranking official in North Korea, said the drills were aggressive and provocative, according to a report in state media Wednesday.

Pak said the name of the exercises harks back to Operation Desert Storm, the US-led military assault on Iraq in 1990-1991 after it invaded Kuwait.

"If the US and South Korea attempt to use armed forces against the (Democratic People's Republic of Korea) without any fear, the special means of the DPRK's armed forces will carry out their strategic mission without delay," he said.

"The US and South Korea will have to face a terrible case and pay the most horrible price in history."

- 'Unstable situation' -

One of the missiles on Wednesday landed in waters just 57 kilometers (35 miles) east of the South Korean mainland, the military said.

"In protest of the joint US-South Korea drill, Pyongyang seems to have staged the most aggressive and threatening armed demonstration against the South since 2010," Cheong Seong-chang, a researcher at the Sejong Institute told AFP.

In March 2010, a North Korean submarine torpedoed the South Korean naval vessel Cheonan, killing 46 sailors including 16 who were on their military service.

In November the same year, the North shelled a South Korean border island, killing two marines -- both of them young conscripts.

"It is now a dangerous and unstable situation that could lead to armed conflicts," he added.

The test follows a recent blitz of launches, including what the North said were tactical nuke drills, that Washington and Seoul have repeatedly warned could culminate in another nuclear test -- which would be Pyongyang's seventh.

The Vigilant Storm air drills were preceded by 12 days of amphibious naval exercises.

"As far as I can remember, North Korea has never made such a provocation when South Korea and the US were holding their joint drills," Park Won-gon, a professor at Ewha University, told AFP.

"Pyongyang seems to have completed its most powerful deterrent. This is a serious threat. The North also seems confident in their nuclear capabilities."