China builds higher fences over fears of instability in North Korea

Fences more than 13ft high, topped with barbed wire, are now being erected along an eight-mile stretch of the Yalu river around the Chinese city of Dandong. This is a popular escape point for North Korea refugees seeking food or better lives, Korea's Yonhap news agency reported.

"It's the first time such strong border fences are being erected here. Looks like it is related to the unstable situation in North Korea," a resident said of the work which began last November but is ongoing.

Previously the border was only marked by a 10ft-high fence which "anybody could cross if they really wanted", the resident added.

Fears for the stability of North Korea have been heightened in recent weeks with reports of a growing food crisis following the severest winter in 60 years and an outbreak of foot-and-mouth disease that has hit the oxen that are still mainly used to plough the North's fields.

This week, in a highly unusual step, foreign aid agencies based in Pyongyang issued a joint statement warning that 6 million North Koreans now need urgent food aid because crops of potatoes, wheat and barley have all failed.

The groups, which include Save the Children and the Swiss government's relief agency, warn that already-malnourished North Koreans could face a total collapse in the North's food distribution system as early as May.

Earlier this month the UN's World Food Programme warned that the at-risk population urgently needed 475,000 tons of food, including cereals and soya beans, to increase protein in the diets, but warned of the risk of corruption in distribution channels.

North Korea experienced a widespread famine in the second half of the 1990s that is estimated to have killed up to a million of the country's 22m-strong population.

In the past North Korea has relied on massive food aid from South Korea – the so-called "sunshine policy" – but the aid has now stopped after attacks by North Korea soured relations between the two countries.

World Food Program officials briefed the South's government on Wednesday about the growing food needs in the North, however Seoul has made it clear that it will not resume aid to the North until Pyongyang takes responsibility for past attacks.

These also include the torpedoing of a North Korea warship, the Cheonan, last March with the loss of 46 South Korean sailors, an act which the North denies.

China has tried to urge North and South to restart stalled peace talks, warning that failure to negotiate with Pyongyang could destabilise North Korea, plunging the country into chaos and precipitating a flood of refugees across the border it is currently reinforcing.

However in a sign that Seoul intends to keep up the pressure on Pyongyang, its armed forces conducted live-fire exercises on Yeonpyeong, the same island where two marines and two civilians were killed in a North Korean artillery bombardment last year.