SEOUL - Hours after North Korea flew a ballistic missile over neighbouring Japan on Tuesday, residents in a South Korean seaside town were startled to see flames leaping from a nearby military base and missiles soaring into the sky.

It was not the start of a war, but a South Korean display of military force that went wrong in a blaze of burning rocket fuel.

Intended as demonstration to deter North Korea, South Korea said it was conducting a nighttime drill with Hyunmoo-2C short-range ballistic missiles (SRBMs) when one failed shortly after launch and hit the ground inside the base in Gangneung, a city with a population of around 200,000 on South Korea’s east coast.

The missile was carrying a warhead, but it was not armed and did not explode, and there were no casualties, a military official told a briefing. The official apologised for causing residents to worry.

The burning rocket fuel lit up the night sky, however, sparking calls to emergency responders and fuelling social media rumours that went unanswered for eight hours until the military disclosed the drill and explained the fire.

“All of a sudden I heard a roar and it made me think something has gone wrong,” said resident Kim Hee-soo. “So I looked at the area where they’ve fired Hyunmoo missiles before and there was flame and smoke and it was a total mess.”

A video that Mr Kim shared on social media went viral overnight, and other residents chimed in with concerns and fears amid silence from military authorities.

“I thought it was a war,” one said in a comment on the video.

Another said their house was shaken by the blast, and a third said they evacuated, thinking that a landslide was headed for their home.

In densely populated South Korea, military training is often conducted near communities, sparking some protests.

The 24-hour disaster management office in Gangneung told Reuters that it had received several calls from worried residents.

An official with the office said the military had confirmed it was conducting a drill, but did not explain the fire, and no city firefighters were called to the base.

"At first we didn't know what was going on because we didn't receive any notice from the military about such training," a city hall official said, speaking on condition of anonymity.

Mr Kim said he is used to missile launches from the base, including a joint United States-South Korea daytime drill in June in response to other North Korean tests.

“I’ve never experienced such an accident in my years having been born and raised here,” said Mr Kim, 43. “It makes me very nervous and I hope that they can let us know whenever they conduct a training.”

South and North Korea remain technically at war after the 1950-53 Korean War ended in an armistice rather than a peace treaty.

Armed conflicts between the two neighbours are rare, but the missile crash made some residents believe that war had broken out.

Said a Twitter user: "What took them so long to confirm? If there is a war, we will probably find out about it the next day."

South Korea's Joint Chiefs of Staff said there were no reported casualties and that it was looking into the cause of the crash. REUTERS, AFP