A North Korean soldier has made a rare bid to defect to South Korea by crossing the demilitarised zone (DMZ) separating the two countries.

The teenager walked up to a South Korean guard post in Gangwon province's Hwacheon county around 8am local time (11pm GMT) after walking across the world's most heavily militarised border.

No gunfire was exchanged as the soldier approached guards and expressed his wish to defect, officials from the South Korean Defence Ministry said.

"We've confirmed his will to defect after he reached our guard post," a ministry spokesman said.

The soldier was taken into custody and an investigation has been launched by South Korean officials.

More than 1,000 North Korean soldiers defect to the South ever year, although it is rare for anybody to attempt to cross the heavily mined DMZ.

Most defectors travel to South Korea via China. The last crossing via the DMZ took place in 2012.

Lee Yun-keol, chairman of the North Korea Strategy Information Service, said: "We had recently heard news that North Korea has been installing mines around the DMZ to prevent people from fleeing to South Korea."

"Also, since the 38th parallel was drawn, only a little over 10 people have succeeded to cross over to the South through the DMZ."

Struggle to adjust to South Korea

The DMZ is 4km wide and is fortified with landmines and barbed wire.

Defectors have previously told of their lives inside North Korea and their difficult journeys to flee the country.

Casey Lartigue is the co-founder of the volunteer organisation Teach North Korean Refugees (TNKR), an NGO that connects North Korean refugees with people who can help them.

Mr Lartigue said many defectors struggle to adjust to South Korean society.

"They have made it to South Korea - a challenging process, not everyone survives - and they often suffer hardship along the way," he said.

"From what I hear, South Korea certainly welcomes them, but after getting out of North Korea, they don't consider themselves to be limited to South Korea."

"While saying they are thankful to have escaped North Korea and to have been accepted by South Korea, they will still say that South Korea is more of a struggle than they imagined."

The defection comes as North Korean leader Kim Jong-Un witnessed the testing of a new anti-ship rocket.

South Korea announced that the North had fired three KN-01 missiles from its eastern border town of Wonsan in to the East Sea on Sunday.

Mr Kim hailed the rocket as "another fresh milestone" in bolstering the country's naval power following the testing of a submarine-launched ballistic missile (SLBM).

The South's defence ministry said the North had tested three short-range missiles with a range of nearly 100km on Sunday off its east coast.

"North Korea appears to be developing new missiles that would replace its old Soviet-designed anti-ship missiles," ministry spokesman Kim Min-Seok told reporters.