This photo taken from the South Korean side of the border shows two trash-carrying balloons flying from North Korea toward the South, Sept. 5. Yonhap

North Korea floated trash-carrying balloons into South Korea for a second straight day on Thursday, South Korea's military said, the latest in its repeated provocations Seoul condemned as "senseless."

"As (North Korea) has again been floating balloons since 9 a.m., we advise the public to beware of falling objects and report to nearby military units or the police when discovering a fallen balloon," the Joint Chiefs of Staff (JCS) said in a notice to reporters.

The move came after North Korea sent around 420 trash-carrying balloons from Wednesday night to early Thursday in what marked its resumption of its balloon campaign after a near monthlong halt.

Around 20 balloons were retrieved in Seoul and the surrounding Gyeonggi Province, with most of them containing scrap paper and plastic bottles, the JCS said. No hazardous substances have been found.

Since late May, the North has launched thousands of balloons carrying trash in a tit-for-tat move against anti-Pyongyang leaflets sent by North Korean defectors and activists in South Korea. Pyongyang last launched such balloons on Aug. 10.

In response to the North's campaign, South Korea's military began blasting anti-Pyongyang propaganda broadcasts daily through loudspeakers on the border in July.

North Korea has bristled against the anti-Pyongyang leaflet and loudspeaker campaigns on fears that an influx of outside information could pose a threat to the Kim Jong-un regime.

South Korea's unification ministry in charge of inter-Korean affairs condemned the repeated balloon campaign as "senseless."

"It is regrettable that North Korea has repeated the senseless and vulgar action at a time when damage from heavy rains is grave," a ministry official told reporters on condition of anonymity.

North Korea is struggling to recover from massive flood damage in its border areas along the Amnok River. Heavy rains in late July flooded large areas of the country's North Phyongan, Jagang and Ryanggang provinces.

The official also stressed that civilian activists' voluntary action to disperse information into the North can never be used as a pretext for North Korea's provocations against the South, referring to the anti-Pyongyang leafleting.

Thursday's move marked the 13th incident in which North Korea floated trash-carrying balloons across the border since late May. (Yonhap)