By Paul-Marin Ngoupana

BANGUI (Reuters) - Residents of Central African Republic's riverside capital Bangui fled in overloaded cars and boats on Friday and others stockpiled food and water as rebels forces paused at the city gates for ceasefire talks.

An insurgency has swept across much of the poverty-stricken but resource-rich former French colony since December 10, posing the biggest threat yet to President Francois Bozize's nearly 10 years in power and threatening a humanitarian crisis.

The government on Thursday urged Western powers France and the United States to help push back the rebel forces, though Paris said it would not use soldiers to defend Bozize's government and Washington evacuated its embassy.

"Our last chance, our only chance, is dialogue with the rebels," said Jerome Lega, a bus driver, as he weaved through traffic in the center of town.

Scores of wooden boats piled high with baggage and people crossed the Oubangui River toward Democratic Republic of Congo on the other side, while the main road south away from rebel lines was choked with overladen vehicles.

Those remaining said they were hoarding food and water and praying international mediation efforts would convince the insurgents not to enter the city shooting.

"We are hoping that Bangui will not be attacked," said Eugenie Bosso, a woman running a market stall.

Envoys from across central Africa arrived in Bangui on Thursday to lay the groundwork for peace talks with the rebels, and regional foreign ministers were due to meet in Gabon later on Friday to discuss the crisis.

A spokesman for the SELEKA rebel coalition - which said it will oust Bozize unless he honors a previous rebel peace agreement that provided payments to former fighters - said on Thursday that it would halt its advance short of Bangui to allow for the mediation efforts.

A diplomatic source said the rebels had reinforced positions around the city, effectively surrounding it.

The rebel advance has highlighted the instability of a country that has remained poor since independence from France in 1960 despite rich deposits of uranium, gold and diamonds. Average income is barely $2 a day.

French nuclear energy group Areva mines the Bakouma uranium deposit in the CAR's south - France's biggest commercial interest in its former colony.

The U.N. Security Council on Thursday said it condemned the rebel advance. Regional and western powers have been pushing for a negotiated solution.

Neighboring Chad has sent troops to help bolster CAR's weak army though it is unclear whether they would be enough to halt a renewed rebel assault on the capital.

The SELEKA coalition brings together three former rebel groups that had largely been contained in CAR's northwest by government forces in recent years, but with foreign backing.

Paris in 2006 defended Bozize's government from a rebel advance using airstrikes. President Francois Hollande on Thursday poured cold water on the latest request for help.

"Those days are over," he said.

Government soldiers were deployed at strategic sites and French troops reinforced security at the French Embassy after protesters threw rocks at the building on Wednesday.

With a government that holds little sway outside the capital, some parts of the country have long endured the consequences of conflicts in troubled neighbors Chad, Sudan and the Democratic Republic of Congo spilling over.

The Central African Republic is one of a number of nations in the region where U.S. Special Forces are helping local forces try to track down the Lords Resistance Army, a rebel group responsible for killing thousands of civilians across four African nations.

(Writing by Richard Valdmanis; Editing by Angus MacSwan)