South Korean activists floated hundreds of thousands of leaflets across the border into North Korea on Friday, protesting Pyongyang's recent missile testing efforts in defiance of UN sanctions.

"We launched the leaflets to protest against these provocative acts," North Korean defector-turned-activist Park Sang-Hak told AFP.

A total of 300,000 leaflets -- along with 2,000 one-dollar bills designed to encourage people to pick them up -- were floated over the heavily militarised border in packages attached to large helium balloons.

The balloon launch came a day after the North conducted what appeared to be its second failed test in a week of a powerful medium-range missile that experts warn could be operationally deployed as early as next year.

The missile -- believed to be an intermediate-range Musudan -- exploded shortly after lift-off early Thursday, according to South Korean and US monitors.

Friday's balloon launch was the first this month by Park's group which has carried out nearly 20 similar exercises this year.

The North's official media has described Park as "human scum without an equal in the world", and threatened to shell areas where the launches are made from.