SEOUL (REUTERS) - A teenaged North Korean soldier walked across the world's most heavily militarised border on Monday in a bid to defect to South Korea, South Korean Defence Ministry officials said.

While there are more than a thousand defections from North Korea to South Korea every year, most defectors come via China and it is rare for a North Korean to cross the heavily mined Demilitarised Zone (DMZ). The last such crossing was in 2012.

The soldier approached a remote South Korean guard post in Gangwon province's Hwacheon county, in the central area of the peninsula, at about 8am on Monday, one Defence Ministry official said.

There was no exchange of fire or warning shots as the soldier clearly expressed his desire to defect, the official said.

The soldier was being held in custody while officials ran checks.

Stretching across the Korean peninsula, the DMZ is 4km wide and is fortified with landmines and barbed wire. There are telephones on the South Korean side for defectors from the North to call seeking help.

Yonhap News Agency reported that the North Korean military had been laying landmines along parts of the border this year, in an apparent move to prevent defections, citing a South Korean government official.

South Korean's defence ministry declined to confirm the report.