North Korea has attempted to fire a missile but the launch was a failure with the enormous weapon blowing up almost immediately after it was set off.
It is thought to be one of the country's new "game-changer" intercontinental ballistic missiles (ICBM) which was paraded in front of the world in a display of military might just hours before.
The South Korean defence ministry said it had detected a failed launch from Sinpo - where North Korea's biggest submarine base is located.
According to a military official the weapon is "presumed to be a new ICBM"as it is longer than the existing KN-08 or KN-14 missiles.
The South Korean defence ministry said in a statement: "North Korea attempted to test an unidentified type of missile from Sinpo area in the South Hamkyong Province this morning, but we suspect the launch has failed."
In a statement, the US military said: "U.S. Pacific Command detected and tracked what we assess was a North Korean missile launch at 11:21 a.m. Hawaii time April 15.
"The launch of the ballistic missile occurred near Sinpo.
"The missile blew up almost immediately. The type of missile is still being assessed.
"U.S. Pacific Command is fully committed to working closely with our allies in the Republic of Korea and in Japan to maintain security."
It comes just hours after North Korea unveiled new weapons during a display of the country's military might as Kim Jong-Un warned of an "annihilating strike" if the US attacks.
President Donald Trump had previously pledged to "take care" of the issue following his surprise cruise missile attack on Syria over its use of chemical weapons.
Meanwhile Pyongyang threatened "catastrophic consequences" when Trump sent an armada of warships to the Korean Peninsula.
At the same time, China has moved 150,000 troops to its border to deal with a possible influx of North Korean refugees amid fears Trump may strike Kim following the surprise US missile attack on Syria last week.
The intercontinental ballistic missiles (ICBM), which Pyongyang claim could travel thousands of miles, have increased concerns that the secretive state is preparing for a possible attack on Washington after they were paraded during the country's Day of the Sun celebrations.
Meanwhile US Vice President Mike Pence is due to land in the South Korean capital Seoul in hours for a 10-day trip to Asia.
Just hours before the apparently failed launch a gleeful Kim, wearing a Western-style suit at Kim Il-sung Square, saluted formations of soldiers who yelled out "long live" to celebrate the 105th anniversary of his grandfather's birth.
The two new kinds of ICBM were enclosed in canister launchers mounted on the back of transporter erector launcher trucks as they were paraded in front of crowds during today's festivities.
Pyongyang has yet to formally announce it has an operational ICBM but experts believe they the new rockets could be liquid-fuelled intercontinental ballistic missiles, or an early prototype.
Submarine-launched ballistic missiles were also among the military hardware on show for the first time.
It indicates an improving technological capability that could help it evade anti-missile systems.
Kim has accused President Donald Trump of provoking his nation towards armed conflict with a series of increasingly aggressive moves, including sending the USS Carl Vinson to the Korean peninsula.
One of Kim's top officials, Choe Ryong Hae, today vowed North Korea would "beat down enemies with the power of nuclear justice".
He told the packed-out square: "If the United States wages reckless provocation against us, our revolutionary power will instantly counter with annihilating strike, and we will respond to full-out war with full-out war and to nuclear war with our style of nuclear strike warfare."
In his annual New Year's address, Kim said North Korea's preparations for an ICBM launch had "reached the final stage".
Recent satellite imagery suggests the country could conduct another underground nuclear test at any time.