The rebels have trounced government forces in the country’s central and northern regions, taking many towns and chopping away at the distance between them and a potential overthrow in Bangui, the seat of one of Africa’s weakest governments, in the middle of one of Africa’s most volatile, porous regions.

Central African Republic is sandwiched between some of the most unstable nations on the continent: Chad and South Sudan sit to its north and east, and just south is the Democratic Republic of Congo. Joseph Kony, the leader of the Lord’s Resistance Army and the focus of a global manhunt, is believed to be hiding in the dense forests of southeastern Central African Republic.

Caught in the middle of this maelstrom are the country’s nearly five million civilians, who have been forced to flee their homes for the deep cover of the dense, central African forest dozens of times over the past five decades. In 2007, fighting grew so intense that tens of thousands of people fled into the deeply troubled nations of Chad and Sudan, so desperate were they for some respite from the bloodshed.

“The population is extremely worried because the rebel advance has moved quickly in a short matter of time, and the army is moving backward,” said Sylvain Groulx, head of mission for Doctors Without Borders in Bangui.

Image Rebels have trounced government forces in the country's central and northern regions, and are nearing Bangui, the capital. Credit... The New York Times

The mass exodus raised the specter of a humanitarian crisis.

“You have a population that under the best times of peace have alarming rates of mortality, some of the worst sanitary conditions in the world; health indicators are extremely bad,” Mr. Groulx said. “Now, all of a sudden, when there is fighting, they are out into the field.”