North Korea has fired a salvo of suspected cruise missiles towards the Sea of Japan, according to South Korea's military, in a major show of force on the eve of a key state anniversary in the North and parliamentary elections in the South.

The back-to-back launches from the ground and air on Tuesday were the most high-profile among a series of weapon tests that North Korea has conducted recently amid stalled nuclear talks and outside worries about a possible coronavirus outbreak in the country.

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North Korean troops based in the eastern coastal city of Munchon in Kangwon province first launched several projectiles - presumed to be cruise missiles - on Tuesday morning, South Korea's joint chiefs of staff (JCS) said in a statement.

The weapons flew more than 150 kilometres (93 miles) off the North's east coast, the JCS said.

If confirmed, it would be North Korea's first cruise missile launch since June 2017, said a South Korean defence official, who spoke to The Associated Press news agency on condition of anonymity, citing department rules.

North Korea also flew multiple Sukhoi-variant and MiG fighter jets above the eastern coastal city of Wonsan, which fired multiple air-to-ground rockets, a spokesman for the South Korean military told AFP.

"South Korea and US intelligence authorities are closely analysing related issues," the JCS statement said.

The launches came a day before North Korea marks the 108th birthday of its late founder, Kim Il Sung, the grandfather of current leader Kim Jong Un. They also came a day ahead of South Korean parliamentary elections.

In recent weeks, North Korea has test-launched a variety of missiles and other weapons amid deadlocked nuclear negotiations with the United States. Last month, it fired nine ballistic missiles in four rounds of tests, according to analysts.

It is unusual for Pyongyang to launch cruise missiles, and most of the weapons it had tested recently were ballistic missiles or long-range artillery shells.

With Tuesday's launches, North Korea was demonstrating that it had "various options" when it came to weapons delivery systems, said Cha Du-Hyeogn, a senior researcher at the Asan Institute for Policy Studies.

"Ballistic missiles demonstrate destructive power while cruise missiles show accuracy," he told AFP. "Until now North Korea has shown its force, and now it is demonstrating accuracy in striking targets."

In June 2017, North Korea hailed the successful test of what it called a new type of surface-to-ship cruise missile designed to hit "any enemy group of battleships" that threatened the country.

That launch hit targets in the Sea of Japan, it said, and took place the week after two US aircraft carriers, the USS Carl Vinson and USS Ronald Reagan, took part in naval manoeuvres in the area.

Those missiles flew about 200km (124 miles), which analysts said was an improvement on a 2015 test that flew only 100km (62 miles).

On Sunday, North Korean state media reported Kim had visited an airbase and observed drills by the country's fighter jets and attack aircraft.

North Korea is subject to multiple United Nations Security Council sanctions over its banned weapons programmes.