North Korea has launched a projectile believed to be a ballistic missile, according to South Korea.

The missile is reported to have flown for 700 kilometres (435 miles) before landing in the Sea of Japan, South Korea's military said.

It comes just days after the election of a new South Korean president and as US, Japanese and European forces gather for military exercises in the Pacific.

South Korea's Joint Chiefs of Staff confirmed the early morning launch but had few other details, including what type of ballistic missile was fired.

A statement said that the missile was fired from near Kusong City, in North Pyongan province, and that the South Korean and the US military are analysing the details.

The kind of projectile matters because while North Korea regularly tests shorter-range missiles, it is also reported to be working to master the technology needed to field nuclear-tipped missiles that can reach the US mainland.

The Trump administration has called such North Korean efforts unacceptable and has swung between threats of military action and offers to talk as it formulates a policy.