Sporadic gunfire and explosions have been reported as M23 rebels advance towards a key city in eastern Democratic Republic of Congo, in an offensive that has forced thousands to flee across the border into Burundi.

Residents and military sources said soldiers were fleeing the assault on Uvira, the last government-held city in the mineral-rich region. US President Donald Trump brokered a peace deal last week between DR Congo's President Félix Tshisekedi and Rwanda's Paul Kagame to end the long-running conflict.

Shops and schools have closed, with terrified residents staying indoors amid fears that rebels had taken control of some government buildings. But South Kivu Governor Jean-Jacques Purusi dismissed reports that the rebels were in the city as 'completely unfounded rumours'.

Residents told local media that the rebels were patrolling central Uvira under the cover of darkness on Tuesday night, while the city remained deserted early on Wednesday.

A local rights official warned of a 'risk of a massacre' if the remaining soldiers mounted strong resistance. Observations from military sources reported that the rebel fighters advanced from the north, near the Burundian border.

In a national address, President Tshisekedi accused Rwanda of 'deliberate violations' of the peace accord, stating that the ongoing conflict threatens to destabilize the entire region, especially given DR Congo's rich mineral resources.

About 200,000 people have fled their homes since the recent fighting began, with international calls for an immediate ceasing of hostilities growing louder as the situation continues to escalate.