Aid groups warn there's a race against time to stop the spread of famine in South Sudan before the rainy season hits.
Oxfam says money is needed urgently otherwise 5.5 million people will go hungry by July.
Authorities this week officially declared more than 100,000 people in two counties of Unity state are experiencing famine while an additional one million are on the brink of starvation.
The United Nations fears there could potentially be genocide because the country is increasingly split along ethnic lines.
Australian Oxfam aid worker Emma Jane Drew last year travelled to the worst hit part of the country.
It was a camping trip she will never forget.
But it wasn't the torrential rain and flooded tents that made it memorable.
She paddled a canoe five hours through the Sudd swamplands to reach remote islands where thousands of families are hiding from the fighting in South Sudan's civil war.
"There was a woman that I met who was foraging through the swamp for wild grasses and lilies to eat, and she was telling me she didn't even own a cooking pot," Ms Drew told AAP from the capital Juba.
"She had been displaced five times ... she lost three of her five children along the way."
The civil war has raged since 2013.
As her team paddled through the marshland, before night fell and they set up camp, Ms Drew was struck by the quiet and inactive children.
"You don't turn up on these islands and see kids running around and playing and having fun," she said.
Ms Drew said in addition to famine, some communities are grappling with cholera, a diarrhoeal disease that could kill within hours.
The federal government made a $14 million food aid contribution to South Sudan and Somalia in January, and is closely monitoring the crisis.
