Millions of Sudanese displaced by Africa's longest war are now returning to southern Sudan, putting pressure on scarce resources in one of the poorest regions in Africa.
Many southerners felt it was to time leave after riots in Khartoum
Many are coming from refugee camps in neighbouring countries, but the largest number were displaced to camps inside Sudan itself, mostly around the capital, Khartoum.
It is the largest movement of people in recent history. Nobody knows how many will come: the highest estimate is six million.
A peace deal was signed between the north and the south in January. But the return of those who fled north to escape the fighting began in earnest only after riots in Khartoum following the death of John Garang, the guerrilla leader who had signed the deal with the north.
Mr Garang died in a helicopter crash in August.
Southern Sudanese mobs rampaged through Khartoum, burning cars and property and killing people, when news broke of his death.
Gangs of northern youths then retaliated, destroying property in the camps housing southerners around the city.
Arriving on the quayside in the southern town of Malakal, John Gideon Jok said he decided to leave Khartoum only after his barber's shop was burnt down in the riots.
It took two long bus journeys and an 18-hour boat trip up the Nile to bring him to his home town, which he had not seen for many years.
His 23-year-old wife, Faiza, was born in the north and had never seen the south, her "homeland", before.
Faiza had hundreds of bites from malaria-bearing mosquitoes after their exposed journey, and one of their children could not open her eyes because of an infection.
Other travellers had suffered even more.
Although regular armies are no longer fighting, thousands of armed men in militia bands still roam the countryside, preying on vulnerable travellers. There have been many accounts of rape and robbery.
Starting from scratch
In a village in the Nuba mountains, a woman showed a wound on her forehead where she said she had been grazed by a bullet while travelling south.
The death of John Garang prompted protests in Khartoum
The bus she was on was shot at and looted by a gang wearing army uniforms and masks to conceal their identities.
She was robbed of all she had saved in the camps, and cannot afford to educate her children.
She lives in one of the rare villages where there is a school.
Kenya is now providing English-speaking teachers, and training Sudanese teachers to construct the education system of the south from scratch. It will be a huge task.
Children who have been to northern schools where they teach in Arabic will have to start again.
Manuel da Silva, the UN official responsible for humanitarian affairs in Sudan, says that the task is not "reconstruction but construction".
Southern Sudanese rebels spent decades fighting the government
He was a minister in the first post-war government in Mozambique after the civil war there, and has recent experience in Liberia - but he says that building southern Sudan is a much bigger task than either of those.
Wary of poor people moving into camps in the south and becoming dependant on aid, the UN is not promoting returns yet.
But it is trying to react quickly since people are coming anyway.
Riek Machar, a warlord turned politician who is now building the new government of the south, says that when the dry season starts in November, people will come as if in a tidal wave.
"We expect a tsunami. There will be a rush. It is their home. If they choose to come back to southern Sudan nobody can prevent them," he said.
'No time to wait'
But the UN's appeals for aid to the south have been hampered by what it calls the "Darfur effect".
The immediate humanitarian crisis of Darfur soaks up emergency funding, and it is hard to persuade some donors to give to other projects in Sudan while the government in Khartoum is held responsible for the continuing violence in Darfur.
Poverty plagues the parts of south Sudan the refugees are bound for
Dennis McNamara, the most senior official to visit the region, is responsible for policy on internally displaced people worldwide.
He says that the response of donors now to peacekeeping and nation-building in the south has not matched the very considerable investment in making the peace in the first place.
The UN says it needs $680m (£385m) for southern Sudan. But it has received pledges for less than half of that.
Mr McNamara is sure that it will come eventually, but he says: "We can't wait for two to three years because the people are not going to wait.
"They're coming back to very little or virtually nothing in some cases."