Footage filmed late on Sunday showed flashes of light in the night sky and the sound of gunfire near the city of Goma.
As heavy fighting continues in the eastern Democratic Republic of Congo, M23 rebels early on Monday claimed to have captured the regional capital.
Their statement came minutes before a 48-hour deadline expired that had been imposed by the group for the Congolese army to surrender their weapons.
The United Nations described “mass panic” among the city’s two million inhabitants.
Goma has also been the last safe haven for thousands of people who have fled intense fighting in the region over the past few weeks.
Rebels urged residents of Goma to remain calm and for members of the Congolese military to assemble at the central stadium.
Congo’s government says the rebel’s advance amounts to was a “declaration of war”.
The M23 rebels’ offensive in the heart of the mineral-rich region threatens to dramatically worsen one of Africa’s longest wars and further displace civilians.
The United Nations says over a third of the population of North Kivu province where Goma is located are currently displaced and the capture of the city will likely exacerbate the situation.
