GOMA, Democratic Republic of the Congo: A humanitarian crisis is looming in eastern Democratic Republic of the Congo, aid agencies have warned, after another day of fighting sent thousands of people fleeing for safety.

The rebel militia M23 - widely believed to be backed by Rwanda - holds the city of Goma but was taken by surprise on Thursday in the village of Sake, 26 kilometres away, when government soldiers launched a counteroffensive.

At Mugunga, a sprawling refugee camp halfway between Goma and Sake, the numbers of displaced seeking shelter have soared.

''Before [the fighting] we had 15,000 people here,'' Jean Sindi Dunia, the principal police commissioner in Mugunga's third camp said. ''Now we have displaced people arriving from Kanyaruchina [another camp north of Goma]. We … think the numbers have tripled.''

Those fleeing find only overcrowded, unsanitary conditions in the poorly supplied camps.