North Korea fired two cruise missiles Wednesday, Seoul's defence ministry said, ending a month-long lull in Pyongyang's record-breaking spate of weapons tests this year.

"Early this morning, we detected that North Korea fired two cruise missiles into the West Sea from Onchon, South Pyongan province," a ministry official told AFP.

"The US and South Korean military authorities are analysing detailed specifications such as flight distance."

North Korea has not tested a cruise missile -- which are not banned under United Nations sanctions on the country -- since January, the Yonhap News Agency reported.

The last time Pyongyang conducted a weapons test was July 10, when they fired what appeared to be multiple rocket launchers.

North Korea has conducted a blitz of sanctions-busting tests since January, including firing an intercontinental ballistic missile at full range for the first time since 2017.

Washington and Seoul officials have also warned that the isolated regime is preparing to carry out what would be its seventh nuclear test.

Earlier this week, South Korean and American military troops kicked off preliminary drills ahead of the start of their annual combined Ulchi Freedom Shield (UFS) exercise.

The drills infuriate Pyongyang, which views them as a rehearsal for invasion.