News of the incursion of the "object" had put the world on edge on Tuesday evening, amid heightened tension over the unpredictable North Korean leader Kim Jong-un's missile launches.

Eight missiles have been fired in violation of United Nations Security Council resolutions this year, the latest on Sunday.

Early reports of a "projectile" soon turned to the possibility the unidentified object was a drone.

The South Korean military said on Wednesday morning around 10 objects had appeared on its radar. They were now believed to have been balloons carrying propaganda leaflets.

Yonhap reported the Ministry of Defence said that several of the flying objects had crossed the demilitarised zone.

"Judging from the results of an analysis, (we) believe there is a low possibility that the objects were drones," the ministry's spokesman Moon Sang-gyun said on Wednesday.

South Korea is on edge as the UN Security Council discusses a resolution to impose new sanctions on North Korea.

Potentially complicating the next step by the international community, the new South Korean government of Moon Jae-in has signaled a new "dual" approach to North Korea, which would include dialogue with North Korea.

This week Moon's government said it would look to resume inter-civilian exchanges between North Korea and South Korea in a way that didn't compromise the international sanctions regime, saying " it is not desirable for inter-Korean relations to continue to be soured".

The South Korean government has also said this week it was a long term goal to reopen a joint industrial park and tour program with North Korea.

A South Korean envoy is due to meet Russian President Vladimir Putin on Wednesday.

A Yonhap report said the envoy is discussing "trilateral cooperation" between Russian, North Korea and South Korea to be pushed forward independently of the nuclear issue.