East and southern African leaders at a summit on Saturday called for an "immediate and unconditional" ceasefire within five days, fearing the conflict, which has killed thousands and driven vast numbers from their homes, would spill over into neighbouring countries.

The M23 has in recent months swiftly seized tracts of territory in mineral-rich east DRC after again taking up arms in late 2021.

Clashes were taking place Tuesday near the locality of Ihusi, around 70 kilometres (43 miles) from the provincial capital Bukavu and 40 kilometres from the province's airport, according to security sources.

Local sources reported "detonations of heavy weapons".

Congolese army reinforcements are moving towards the town of Kavumu, where the airport is located and which also hosts the army's main military base in the region, according to security sources.

Bukavu has been preparing for an M23 offensive for several days, with schools shuttering in the city Friday as residents began to flee and shops closed over fears of an imminent attack.

The M23, which claims to protect ethnic Tutsis, began advancing in South Kivu after late last month taking control of Goma, the capital of neighbouring North Kivu province that borders Rwanda.

The anti-governmental group has begun setting up its own administration in Goma, a city of one million people, launching recruitment campaigns, including to create a police force.