Justin Welby has warned of the 'dire situation' in South Sudan as a state of famine has been declared in parts of the African nation where an estimated 100,000 people are already starving, according to the UN.

The Archbishop of Canterbury appealed in a Facebook post for new humanitarian corridors for aid to reach people in need in the crisis-ridden country, which has been devastated by three years of civil war.

'We stand prayerfully alongside the South Sudanese people and their leaders,' wrote Archbishop Welby, who is visiting several African countries.

'We pray for those on the ground who are delivering humanitarian assistance, that there will be an opening up of humanitarian corridors for the aid that is so desperately needed.'

The comments come as the UN reports that 275,000 children are severely malnourished and more than 5 million people are urgently in need of food, agricultural and nutritional assistance.

'I've seen first-hand the consequences of the volume of refugees attempting to cross the borders to find safety, and the crisis facing those neighbouring countries as well as those in South Sudan,' Welby said.

The famine in South Sudan is the first to be declared since the Somalian famine in 2011, when more than 250,000 people died from starvation over a two year period.

The Archbishop's intervention came as the international children's charity World Vision is warning that almost 5.5 million people - half the country - will face severe food shortages by July if international donors and governments do not urgently work together.

Perry Mansfield, the National Director for World Vision in South Sudan said: 'The situation facing children who were already hungry and going without meals is now rapidly unravelling. If aid, funding and deliveries are not immediately scaled up we should expect to see children facing starvation.'

She added: 'The rainy season is only weeks away and once that arrives the roads become impassable, meaning that millions of people will be cut off from aid. We have a small and rapidly closing window of opportunity to get food into these remote areas, to preposition it, before it is too late."

World Vision is working in partnership with the World Food Programme to provide food assistance to half a million of the most affected people in various parts of the country.

Separately, Christian leaders in Sudan said that state officials in the country plan to demolish at least 25 churches in and around the capital, Khartoum, according to Morning Star News (MSN).

A letter written in June last year from the Executive Corporation for the Protection of Government Lands, Environment, Roads and Demolition of Irregularities of Khartoum State reveals the names and locations of 25 church buildings marked for demolition. The government reportedly claimed the churches were built on land zoned for other uses, but Christian leaders said it is part of wider crack-down on Christianity, MSN reported.

'This is not an isolated act but should be taken with wider perspective,' said Yahia Abdelrahim Nalu, moderator of the Sudan Presbyterian Evangelical Church's Sudan Evangelical Synod.