North Korea fired two short-range missiles into the sea off the east coast of the Korean peninsula overnight, South Korea's defence ministry has said.

The North launched similar rockets last week.

South Korea's Yonhap news agency said the missiles likely flew about 500km after being launched off the North's east coast, adding they were believed to be Scud-C models.

South Korea's defence ministry has said the Scuds are normally fired using mobile launch pads which can be activated with minimal preparation.

The distance would mean the weapon could hit targets in South Korea and Japan.

Launches by the North of short-range missiles are not uncommon as part of regular military exercises.

The firing came days after the beginning of annual US and South Korean joint military exercises, which the North routinely denounces as a preparation for war.