TURALEI, Sudan - Ayak Adiang and her children will soon run out of food - but only because Adiang opened her home to villagers running from violence.

Tens of thousands of Sudanese are fleeing from the contested north-south border region of Abyei, and the top U.S. official in the region warned Friday of a humanitarian crisis over the north's invasion.

Food and fuel are running short. There is not nearly enough shelter.

Adiang's single-room house is bursting with people. Martha Abiem Deng arrived empty-handed with two relatives and a dozen children between them after fleeing fighting in Abyei. Adiang took them in.

"They will consume the little we have," Adiang said as she sat near the dark, pungent hut that serves as her kitchen.

All Adiang has left is a pot of meat and three bowls of pounded porridge. Turalei's market is empty after an influx of frightened families arrived over the last few days, almost doubling the town's population. The only things still for sale are cigarettes and telephone chargers.

County Commissioner Dominic Deng said Friday that up to 40,000 people had arrived in Turalei, a town just south of Abyei. He said that at least 80,000 people had fled Abyei, a zone about the size of Connecticut that northern Sudan invaded last weekend.

On a visit to Turalei on Friday, the top U.S. official in Southern Sudan, Barrie Walkley, said "we have a perfect storm" creating a humanitarian crisis. Sudan's north is blockading border crossing points, preventing food and fuel from getting to the south. Militias are attacking southern forces, and the northern army displaced tens of thousands of people by invading Abyei, he said.

Lise Grande, the United Nations' top humanitarian official in Southern Sudan, said there were not enough stocks in the area to supply all the fleeing families with food and shelter. The fuel shortage is greatly hampering relief efforts, she said.

"It's double the number of people we were planning for," she said. "We have to face the fact that if they are here for a while, then what we have is not enough."

Outside Adiang's hut, Deng sat under a tree and gestured to one small jerry can. Her whole family must share the water within it.

"We don't have any money, and there is no food in the market anyway," Deng, 49, said.

Both northern and Southern Sudan stake a claim to Abyei, a fertile grassland near several oil fields. Fighting between north and south broke out last week, and northern troops moved in with force.