A malfunctioning South Korean ballistic missile blew up during a live-fire drill with the US which was a reprisal for North Korea's successful launch a day earlier of a weapon that flew over Japan.
The missile fired by Pyongyang on Tuesday had the range to strike the US territory of Guam.
The explosion and subsequent fire from the South Korean missile on Wednesday panicked and confused residents of the coastal city of Gangneung, who were already uneasy over the increasingly provocative weapons tests by rival North Korea.
Their concern that it could be a North Korean attack only grew as the military and government officials provided no explanation about the explosion for hours.
South Korea's Joint Chiefs of Staff said no injuries have been reported from the explosion, which involved a short-range Hyumoo-2 missile that crashed inside an air force base in the outskirts of the city. It said the crash did not affect any civilian facilities.
During the same drill, the US military launched four of its own missiles that are part of the Army Tactical Missile System and South Korea fired another Hyumoo-2 successfully.
Watch: US joins South Korean forces for training amid tensions with the North.
The homegrown missile is key to South Korea's pre-emptive and retaliatory strike strategies against the North and is a version of a Russian-designed Iskander missile, which is also possessed by the North.
Kwon Seong-dong, a ruling party lawmaker representing Gangneung, wrote on Facebook that a "weapons system operated by our blood-like taxpayer money ended up threatening our own people" and called for the military to thoroughly investigate the missile failure.
He also criticised the military for not issuing a notice about the failure while maintaining a media embargo on the joint drills.
"It was an irresponsible response," Mr Kwon wrote. "They don't even have an official press release yet."
South Korea's military acknowledged the missile malfunction hours after internet users raised alarm about the blast and posted social media videos showing an orange ball of flames emerging from an area they described as near the air force base.
It said it was investigating what caused the "abnormal flight" of the missile.
Watch: Exploring North Korea's nuclear weapon capability.
Officials at Gangneung's fire department and city hall said emergency workers were dispatched to the air force base and a nearby army base in response to calls about a possible explosion but were sent back by military officials.
The US and South Korean militaries are conducting the joint exercises to show their ability to deter a North Korean attack on the South. In addition to missile launches, they involved bombing runs by F-15 strike jets using precision munitions.
North Korea's successful launch of a nuclear-capable ballistic missile hours before the drills was the country's most provocative weapons demonstration since 2017 and was its fifth round of weapons tests in 10 days.
That missile has a range capable of striking Guam, which is home to one of the largest military facilities maintained by the US in Asia. North Korea in 2017 also tested missiles capable of hitting the continental United States.