Doctors with Without Borders said more than 800,000 displaced persons were in North Kivu province, up from 500,000 in the province before the latest round of violence, the BBC reported Friday.
The organization said refugees lacked shelter and other basic items, and in some instances, fled from one camp to another in the region that has been plagued for years by violence.
Fighting between government forces and M23 rebels increased last month as the militants seized control of Goma and advanced to other cities.
M23 soldiers were considered part of the Congolese national army under a 2009 peace negotiation. However, they broke from the government army in April, complaining of poor conditions and lack of pay. One M23 commander, Bosco Ntaganda, is wanted by the International Criminal Court for war crimes, including child-soldier recruitment.
The fighting between the M23 rebel group and government troops has quieted recently because has both sides are in neighboring Uganda for peace talks.