North Korea has fired an "unknown projectile" which appeared to fail immediately after launch, South Korea's military said.
The suspected missile was fired from an airfield outside the capital Pyongyang.
The airfield has been the site of several launches, including previous tests of what were the US alleges were intercontinental ballistic missiles (ICBMs).
It comes as North Korea has in recent weeks stepped up its weapons testing.
"North Korea fired an unknown projectile from the Sunan area around 09:30 today, but it is presumed that it failed immediately after launch," Seoul's Joint Chiefs of Staff said in a statement.
Specialist news site NK News cited witnesses as saying loud "blowing" sounds, similar to that of a large aircraft, were audible in Pyongyang, followed by a loud "crash". It added that it had seen an image showing a red-tinted ball of smoke in the sky above the capital.
Speaking to NK News, senior fellow at the Carnegie Endowment for International Peace Ankit Panda said this image was consistent with that of a "catastrophic failure". He added that "reddish-orange smoke" is associated with liquid fuel - something that is "very toxic" to humans.