Aid agencies are attempting to provide assistance to thousands of people displaced by unrest in the east of the Democratic Republic of Congo.
Thousands have already fled recent unrest in eastern DR Congo
United Nations officials estimate at least 20,000 people have fled to North Kivu province from nearby South Kivu.
Local authorities put the number at up to 150,000.
The civilians were fleeing a recent advance by government troops on dissident soldiers, who broke away from the national army earlier this year.
Meanwhile, DR Congo and Rwanda have agreed to set up a UN-backed body to help resolve long-standing security issues on their border, UN officials say.
The agreement was reached in talks at the UN between Secretary General Kofi Annan, Congolese President Joseph Kabila, and Rwandan Prime Minister Bernard Makuza.
The joint verification mechanism will be composed of UN and African Union officials, along with technical experts from both governments.
Instability affects large parts of eastern DR Congo despite a peace deal last year, under which rebels joined a new power-sharing government.
The BBC's Rob Walker in Rwanda say this latest flight of civilians follows a familiar pattern laid down during a decade of violence in the region.
After villagers heard government soldiers were advancing from the south last week, they took what they could carry and started walking north.
The thousands of displaced people are now living out in the open on the cold hills of North Kivu province.
Aid agencies will start trying to deliver relief supplies within the next few days.
Providing shelter will be the first priority.
The government troops were moving against the positions of dissident soldiers led by General Laurent Nkunda.
His forces withdrew without a fight but they remain defiant, and DR Congo's transitional government still has only tenuous control over the east of the country.
UN peacekeepers have been unable to contain the continuing violence there.
Kofi Annan has asked for the current force of 11,000 to be more than doubled.