Some 4,000 people have arrived in the past several days at a UN camp in the eastern Democratic Republic of Congo, the UN refugee agency (UNHCR) says.
Children are being particularly targeted by the rebels, reports say
It says many of those at the Bulengo site had fled troops of rebel Congolese General Laurent Nkunda, who are accused of looting and abducting children.
More than 300,000 people in the area have fled this year, the UNHCR says.
Ethnic tension following the 1994 genocide of Tutsis in Rwanda lies at the heart of the fighting.
The Bulengo site for the internally displaced people had seen some 4,000 people arriving in the past three days, Masako Yonekawa, UNHCR head in the nearby town of Goma, told the BBC News website.
Ms Yonekawa said the site, about 20km (12 miles) west of Goma, was now housing some 10,000 people.
She said that many of those arriving in Bulengo and other sites around Goma were trying to escape from Gen Nkunda's forces, who have been blamed for looting and raping and also mass abductions.
The UNHCR has said children are being forcibly taken from schools to join the rebels, with 280 children reported to have been abducted from one location alone.
Tutsi Gen Nkunda has accused the government of collaborating with rebel Hutu fighters from Rwanda against Tutsi civilians living in the area.
The region saw a brief period of calm when Gen Nkunda and the government agreed to deploy "mixed brigades", made up of the general's men alongside regular army units - but the deal collapsed last month.
Gen Nkunda says his insurgency is not about "toppling the regime" of Congolese President Joseph Kabila.
He says it is about holding the government responsible for its failure to confront the Rwandan Hutu rebels who fled to DR Congo after the 1994 genocide.