A North Korean soldier has fled to South Korea by swimming across the Han River, the second defection in a week.

South Korea's Joint Chiefs of Staff said the man had swum across a particularly narrow part of the fast-moving river after attaching foam to his shoulders to help him stay afloat.

Last week, a North Korean soldier walked across the heavily-guarded border that separates the countries.

Soldiers had previously been defecting at the rate of about one a year.

The latest defector, thought to be in his early twenties, was spotted at Gimpo, just west of the southern capital Seoul, Yonhap news agency reported.

He screamed "Don't kill me, I am here to defect", at a South Korean marine who had seen him, Yonhap said.

The soldier will now be questioned by military officials.

North and South Korea are technically still at war, since the conflict between them ended in 1953 with a truce, not a formal peace treaty.

Seoul says more than 30,000 North Koreans have defected to the South since the end of the Korean War, the majority via China, which has the longest border with the North.