A balloon is found floating on the top of an apartment building in Michuhol district, Incheon, June 9. Yonhap

North Korea has launched around 310 trash-carrying balloons toward South Korea overnight, Seoul's military said Monday, amid escalating tensions over the North's repeated balloon campaign to which South Korea has responded with the resumption of loudspeaker propaganda broadcasts after six years.

The latest batch of waste-loaded balloons sent late Sunday contained scrap paper and plastic, with no toxic material detected so far, according to the Joint Chiefs of Staff (JCS). No additional balloons were detected floating in the air as of 8:30 a.m.

JCS spokesperson Col. Lee Sung-jun said many of the balloons failed to reach South Korea due to the wind blowing in an eastward direction, with around 50 balloons being found across the border.

The North did not did not stage more launches early Monday, but the number of fallen balloons in the South is expected to increase as the military continued to receive reports on them, Lee told reporters in a regular briefing.

Sunday's launch marked the latest in the North's balloon campaign that started on May 28, which it described as a "tit-for-tat" response to anti-Pyongyang leafleting by activists in South Korea. The North is estimated to have launched more than 1,600 trash-carrying balloons so far.

It also came hours after South Korea resumed loudspeaker propaganda broadcasts in the border area after condemning the North's attempts to cause public concern as "unacceptable" and vowed to take "corresponding measures."

Lee said the military did not detect any unusual North Korean military activity after the broadcasts, which lasted for about two hours from 5 p.m. and marked the first since they were halted under an inter-Korean declaration in 2018.

The JCS has warned that whether the broadcasts will take place again will depend on the North's actions.

"Considering the strategic and operational situation, (we) will conduct operations flexibly," Lee said when asked why the military did not resume the broadcasts after the latest balloon launch.

A military source said the South is unlikely to operate the loudspeakers again on Monday, citing the need to manage the situation with the North.

Another government source said the resumption of the loudspeaker campaign the previous day does not necessarily mean the South will conduct broadcasts again on Monday.

Pyongyang has reacted angrily to the broadcasts in the past, firing artillery shots toward the South in August 2015 over the propaganda loudspeaker campaign.

Late Sunday, Kim Yo-jong, the powerful sister of North Korean leader Kim Jong-un, warned that South Korea will face unspecified "new counteraction" should it continue to send anti-Pyongyang leaflets and play loudspeaker broadcasts across the border.

When asked about the statement, Lee said the North Korean military's activities are being closely monitored, and that the military will be able to fully respond to what Kim called a "new counteraction."

"Our military has the capabilities to respond to any North Korean provocation overwhelmingly," he said.

The military source, however, noted that Kim's rhetoric appeared to be less threatening than expected.

"At this point ... (we) need to watch the situation, remain calm and show restraint," the source said.

For years, North Korean defectors in the South and conservative activists have sent leaflets to the North via balloons to help encourage North Koreans to eventually rise up against the Pyongyang regime.

North Korea has bristled at the propaganda campaign amid concern that an influx of outside information could pose a threat to its leader Kim Jong-un.

In 2014, the two Koreas exchanged machine-gun fire across the border after the North apparently tried to shoot down balloons carrying propaganda leaflets critical of North Korea. (Yonhap)