Rebels in eastern Congo pushed south along Lake Kivu after repelling a counter-attack by government forces near the new rebel stronghold in the city of Goma on the Rwandan border.
Others moved north from the strategic road junction at Sake.
Rebels were reported to be in control of Sake after a battle on Thursday, which had been the first sign of a government fightback after the army abandoned Goma on Tuesday to the M23 movement, widely thought to be backed by Rwanda.
Local people and fighters said Congolese troops and allied militia had pulled back from Sake, which lies 20km (12 miles) west along the lake from Goma, to Minova, a further 15km south along the main highway in the direction of M23's stated next objective, the city of Bukavu at the southern tip of the lake.
Fighters for the group, which said after taking Goma that it would march on the capital Kinshasa – 1000 miles away – to defeat President Joseph Kabila, met no resistance as they probed several miles south.
Thousands of refugees were fleeing the fighting and heading for Goma, where aid agencies have a significant presence, along with UN peacekeepers who stood back when the rebels moved in.
Previous uprisings in the Democratic Republic of Congo, among them one led by Mr Kabila's father, have been launched from the area, where a mix of colonial-era borders, rich mineral deposits and ethnic rivalries has caused millions of deaths during nearly two decades of turmoil since the 1994 genocide in Rwanda.
Regional leaders are due to hold crisis talks today in Kampala, capital of neighbouring Uganda.
A Congolese government spokesman confirmed Mr Kabila would return to Uganda on Saturday.