The United Nations has withdrawn its non-essential workers from El Fasher, capital of Sudan's North Darfur state.
Those in camps near El Fasher will be more isolated
The UN said the move is temporary until the risk of fighting between Arab Janjaweed militia and rebels subsides.
The African Union has warned that El Fasher is at risk of being attacked by a coalition of Darfuri rebel groups.
At least 200,000 people are estimated to have died and more than two million driven from their homes since the conflict began in 2003.
"The schools have shut down and all the markets are closed," a resident told Reuters news agency, speaking on condition of anonymity. "People are worried."
The aid workers were relocated "as a result of increased Janjaweed presence in the town and armed movements in the area", said Radhia Achouri, spokeswoman for the UN mission in Sudan.
Janjaweed militia and rebel fighters clashed in the town's market on Monday, leaving two SLM rebels dead, the Associated Press news agency said.
More than 300 humanitarian workers are based in the town, which is one of two key centres for Darfur's huge aid operation.
Late on Tuesday night a UN plane flew 134 of them out.
Hundreds of thousands of people live in the town or in the camps that surround it, says the BBC's correspondent in Khartoum, Jonah Fisher.
Its airport is the key supply route used by Khartoum to arm and equip government forces, says our correspondent.
An African Union statement said that the town was at risk of being attacked and that its headquarters there was a possible target.
The Sudanese government is still resisting pressure for the UN to take control of the African Union peacekeeping mission in Darfur.
The outgoing UN humanitarian chief Jan Egeland, has said that one of his biggest regrets was that more was not done for Darfur in the early stages of the crisis.
"We're saving really the assets that we can at the moment, protecting the life of our own people," he said of the UN pullout from El Fasher.
"But we're not protecting the lives of the vulnerable women and children and there are four times more of them now than when we started in 2004."