South Korea rocket launch sparks UFO scare after red trail spotted snaking through sky

Hundreds of people called police in South Korea after fearing a rocket test-fired by the military was a UFO or North Korean missile attack.

The South Korean Defence Ministry had kept the launch a secret, but after the public scare explained that they'd been test-firing a solid-fuelled rocket.

The rocket was part of the military's efforts to build a space-based surveillance capability and bolster its defences, it explained.

The ministry said it did not notify the general public of the launch in advance because it involved sensitive military security issues.

A white and red vapour trail could be seen snaking behind a bright white light in parts of South Korea's sky.

The solid-fuel rocket was test-fired by the South Korean military (AFP/Getty Images)

South Korean social media and internet sites were abuzz with messages by citizens who said they saw a soaring object, rainbow-coloured vapour trail or other mysterious lights. Some also posted photos and videos.

South Korean emergency offices and police received hundreds of citizens' reports of witnessing of a suspicious flying object and mysterious lights across the country, according to local media.

The rocket launch came four days after the South accused the North of flying five drones across the rivals' border for the first time in five years.

Its military detected the drones but failed to shoot them down, causing security concerns about its air defence network. The military later offered a rare apology for that.

South Korean officials said they plan to use a solid-fuelled rocket to put the nation's first spy satellite into orbit. In March, South Korea conducted its first successful launch of a solid-fuel rocket.

There were fears the rocket was a missile attack from North Korea, led by Kim Jong-un, pictured (KCNA VIA KNS/AFP via Getty Image)

Solid-fuel rockets reduce launch times, have simpler structures and are cheaper to develop and manufacture than liquid-fuel rockets, South Korean officials said.

The Defence Ministry said Friday's launch was a follow-up test of the March launch.

North Korea is also pushing to develop its first military surveillance satellite and other high-tech weapons systems to cope with what it calls US hostility.

Earlier this year, North Korea performed a record number of missile tests in what experts call a bid to perfect its nuclear weapons technology and boost its leverage in future dealings with the United States.