North Korea fired what were believed to be cruise missiles off its east coast in an unusual military drill, and air-to-ground missiles from fighter jets into the sea between the Korean peninsula and Japan, South Korea's military said on Tuesday.

The barrage of missile tests may have been timed to mark the eve of the birthday of the nation’s late founding father, Kim Il Sung, and the South’s parliamentary elections.

The combination of the two military exercises was described on Twitter by Melissa Hanham, deputy director of the Open Nuclear Network in Vienna, as “one of North Korea’s larger scale drills to date.”

The latest in a slew of weapons launches over the last few weeks began at 7am local time when surface-to-air missiles were fired from the eastern coastal town of Munchon, travelling 150 km before splashing down.

Separately, the North also flew multiple Sukhoi-variant fighter jets above the eastern coastal city of Wonsan, firing an unspecified number of missiles into the sea, Seoul’s Joint Chiefs of Staff said, adding that they were “closely monitoring” the situation.

The nuclear-armed North has repeatedly tested ballistic missiles in recent years, but it would be unusual for them to launch cruise missiles.

In contrast to ballistic missiles, these travel at low altitude - sometimes just a few metres above the surface - making them hard to detect. Sometimes highly manoeuverable, they need sophisticated guidance systems to bring them to their targets.