Analysts and media reports said the North's test was in response to South Korea's launch of its first destroyer equipped with high-tech Aegis radar technology developed by the U.S. South Korea is now one of only five countries armed with the technology, which will make it easier to track and shoot down North Korean aircraft and missiles.
"This shows North Korea, whose navy is rather small, is extremely alarmed," said Toshimitsu Shigemura, an expert on North Korean issues at Japan's Waseda University.
South Korea's Joint Chiefs of Staff confirmed the missile launches.
"The short-range missile launches are believed to be part of a routine exercise that North Korea has conducted annually on the east and the west coasts in the past," the statement said.
The missiles were fired from the communist country's east coast into the sea between Japan and the Korean peninsula, a Joint Chiefs official said on condition of anonymity, citing official protocol.
Japan's public broadcaster and other media, citing Japanese and U.S. sources, reported the missiles were surface-to-ship. Japan's Defense Ministry and Foreign Ministry could not immediately confirm the reports.
North Korea's missile program has been a constant concern to the region, along with its pursuit of nuclear weapons.
The hard-line regime test-fired a series of missiles in July last year, including its latest long-range model, known abroad as the Taepodong-2, which experts believe could reach parts of the United States. The North rattled the world again in October by conducting its first-ever test of a nuclear device. However, experts believe it does not have a bomb design advanced enough to be placed on a missile.
In Washington, White House spokesman Gordon Johndroe said the United States sees the test "as a routine exercise that they do from time to time." U.S. officials, eager to make progress on a nuclear disarmament accord with the North that has been stalled over a financial dispute, have been hesitant to criticize Pyongyang.
European Union officials said they were concerned North Korea's short-range missile tests posed a further risk to stability in Asia and urged the isolated nation to seek dialogue to ease tensions with its neighbors.
In Japan, Prime Minister Shinzo Abe called the tests "extremely regrettable," but added: "We do not consider (the missile firing) as a serious threat to Japan's national security."
South Korea's Yonhap news agency cited an unidentified Unification Ministry official as saying the tests would not strain ties because they were apparently part of regular exercises. North and South Korea are planning Cabinet level talks on reconciliation efforts next week in Seoul.
Japanese public broadcaster NHK said the missiles were shorter-range, and were not North Korea's existing Rodong or Taepodong I ballistic missiles.
Kyodo News agency said the missiles were launched from Hamgyong Namdo on the east coast of the Korean Peninsula and are considered modified silkworm or miniaturized Scuds with a range of 60-125 miles.
Mobile missile carriers, communication equipment and personnel were seen in the area before the launch, but they left after the missiles were fired, Kyodo said.
Last month, North Korea displayed a newly developed ballistic missile capable of reaching the U.S. territory of Guam during a military parade, the South Korean newspaper Chosun Ilbo reported, citing an unidentified South Korean government official familiar with an analysis of U.S. satellite images.