Refugees displaced by long-running conflicts in Sudan are continuing to flee across the border to South Sudan, but a full-blown health crisis has started to develop in refugee camps as the rainy season begins.

More than 120,000 refugees have fled from conflict in Sudan's Blue Nile State since late last year and are coming to camps in South Sudan's Upper Nile State that aid workers describe as "uniquely unsuited" to accommodating so many people.

Médecins Sans Frontières said almost three children were dying each day at the Jamam camp, mostly from diarrhoea, even before the onset of heavy rains.

Now, they say the mud wasteland has started to turn into a swampy flood plain. Latrines have overflowed, contaminating water on the ground, and many refugees, including children, are sleeping in wet clothes on sodden blankets.

This week ABC News Online spoke to Vanessa Cramond, a nurse from New Zealand working for MSF in Upper Nile State, as she prepared to travel with some of the refugees to a larger camp named Batil.

Children walk through the flooded Jamam camp. ( Shannon Jensen )

Refugees sit in a truck in Jamam camp. ( Médecins Sans Frontières: Corinne Baker )

MSF screens refugees in the rain as they come off a truck from another refugee camp, nicknamed K18. ( Médecins Sans Frontières: Corinne Baker )

Two malnourished children and a pregnant woman in labour are transferred to Jamam camp hospital. ( Médecins Sans Frontières: Corinne Baker )

Jamam's outpatient department sees a busy Monday morning. ( Médecins Sans Frontières: Corinne Baker )

People line up to be transferred to the new camp, Batil. ( Médecins Sans Frontières: Corinne Baker )

MSF workers clean up the clinic in Jamam after a night of rain. ( Médecins Sans Frontières: Corinne Baker )

You can follow Corinne Baker as she photographs her work in South Sudan on Twitter: @RinBaker