North Korea has sent about 500 balloons laden with trash into South Korea's air space over the past 24 hours.

The balloons disrupted flights and ignited a fire on the roof of a residential building in Seoul.

A suspected balloon suspended take-offs and landings at Seoul's Gimpo Airport for two hours.

South Korea's military said some trash balloons were equipped with timed poppers that could cause fires.

On Wednesday, North Korean balloons had landed in the vicinity of the heavily guarded presidential office in Seoul.