South Korean activists have sent tens of thousands of anti-Pyongyang leaflets across the border by balloons into North Korea, one week after warnings from Seoul and threats of retaliation from Pyongyang.

Around a dozen activists attached 50,000 leaflets to seven balloons Monday and sent them floating over the Demilitarized Zone dividing the two countries. Some local residents fearing reprisal from the North scuffled with the activists.

The balloons were launched from the Imjingak resort in the border city of Paju, where South Korean police blocked an earlier launch attempt last Monday.

The North's official Korean Central News Agency said before the first attempt that the Korean People's Army would conduct a “merciless strike” without warning if the leaflets were sent.

However, just hours after the launch was aborted, the activists launched balloons from Ganghwa Island, west of Seoul, with no military response from the North.

North Korea has lashed out at previous balloon launches, threatening to shell South Korea in response to such actions, which it calls deliberate provocation by Seoul that could lead to war. Seoul says it has nothing to do with the launches.