"North Korea fired an unidentified missile from a site in the vicinity of Bukchang in Pyeongannam-do (South Pyeongan Province) early this morning," Yonhap reported, quoting a statement issued by South Korea's military.
The report added that Seoul was analysing the type and flight distance of the projectile.
The launch comes with tensions high on the Korean peninsula, with this the latest in a series of missile launches by the North and warnings from US President Donald Trump's administration that it was running out of patience.