In a pastoral letter from South Sudan Catholic Bishops' Conference they say the nation is gripped by "a humanitarian crisis - famine, insecurity and economic hardship".
A boy has his arm measured to see if he is suffering from malnutrition
UN agencies and South Sudan's government warn that more than 100,000 are experiencing famine in two counties.
Tens of thousands of people have died in a civil war that began in December 2013 and severe inflation has put food beyond the financial reach of many.
The bishops' letter adds: "Our people are struggling simply to survive. While there have been poor rains in many parts of the country, there is no doubt that this famine is man-made, due to insecurity and poor economic management.
"Millions of our people are affected, with large numbers displaced from their homes and many fleeing to neighbouring countries, where they are facing appalling hardships in refugee camps."
Speaking on Premier's News Hour, Bishop William Kenney, who has visited the country, said the West should be preparing to send in peace keeping troops.
"It's probably just a little too early [to send in troops] but that's what they should be heading for.
"I think the answer is to get people to sit round a table, they've done that and it didn't lead anywhere, but it needs power from outside in order to achieve [peace]."
"The violence must stop and the international community must intervene."
He warned that whilst aid agencies like CAFOD had scaled up their response some food was struggling to get through because of the violence.
"You can't just send people out to be shot," he said.
Bishop William Kenney speaking to Premier's Antony Bushfield:
