But Henchi Ordjo, an opposition alliance spokesman, told Reuters news agency on Saturday that fighters had simply held back an assault on the palace to allow Idriss Deby, Chad's president, the opportunity to leave.
"No ceasefire has been agreed," Ordjo said.
The main market in Ndjamena and the national radio station were destroyed Sunday by fires and looting, witnesses told the AFP news agency, as fighting raged between rebels and government forces in Chad's capital.
One witness said: "The public market was partly set on fire in the morning after a helicopter [belonging to government forces] fired a rocket at rebels."
"The start of the fire triggered a panic, after which the crowd came back to ransack the market," he said, as another witness reported that the radio station had been pillaged by a mob that smashed broadcasting equipment and made off with computers.
Bodies in the street
No death toll from the fighting has been given but a UN security service official said there were a lot of bodies in the streets, "some burned, some just hacked" to death.
The Medecins sans Frontieres (MSF, or Doctors Without Borders) aid group said hundreds of civilians had been wounded, but it was unable to give a death toll.
Isabelle Defourny, head of the group's operations in Chad, said an MSF team working in one Ndjamena hospital had treated 48 wounded people on Saturday alone, "only one of them a combattant".
About 400 people had fled across the western border into Cameroon, according to the UN refugee agency.
Al Jazeera's Haru Mutasa, reporting from Njadmena, said that a new round of fighting had broken out early on Sunday.
"It doesn't look like a ceasefire is in place, the fighting is getting closer to where we are," she said.
The new fighting dashed hopes of a ceasefire which Libyan leader Moamer Kadhafi was reportedly trying to secure.
Deby has turned down a French offer to help him escape from the advance, an official source in Paris told AFP news agency on Sunday.
Rebel leaders accuse Deby of ruling like a dictator and favouring his family and friends.
Al Jazeera's Mutasa said that several Chadian soldiers had come to the gates of a hotel where expatriates are holed up in an effort to take refuge, but were turned away by French troops.
"No one knows who is in control, but there are reports that the government is sending in reinforcements to fight the rebels. This is all going on while the French army tries to evacuate French and other foreign nationals," Mutasa said.
She also said that while the evacuations of foreigners were under way, Chadian residents have been left to fend for themselves.
"It was planned that the Chadian army would also protect civilians, but it doesn't seem to be the case now - and they are left to find shelter from from the fighting."
Cameroon authorities said that thousands of refugees from Ndjamena, including foreign diplomats, had fled to the northern Cameroon towns of Kousseri and Maroua.
President Idriss Deby seized power in a Libyan-backed coup in 1990
He went on to win the Chad's first two
multi-party elections in 1996 and 2001
A ceasefire signed between Deby and four rebel groups in October recently collapsed
The largest rebel group, the Union of Forces for Democracy and Development, is led by a former minister who accuses Deby of corruption
Click here for more on Chad's spiral into conflict
"Late last night we counted about 3,000 here. All the inns and small hotels here are full and those who cannot afford then are lodged in a primary school and temporary shelters," Alain Fritz Ndibi, Kousseri senior administration officer, said.
"I can hear gun and mortar fire from across the river."
There has been no official confirmation about the whereabouts of Deby, but two of his ministers said he remained inside the palace complex at the head of loyal troops.
Mahamat Ali Abdallah Nassour, minister of state in Deby's government, told Radio France International (RFI) that Chad's security forces were "in control in the capital".
Chadian army helicopters took off from the military base at the airport and had opened fire on opposition fighters in south Ndjamena, a military source said on Saturday.
A French air force plane began evacuating several hundred French and other foreign nationals to Gabon, an official at the French military base in Ndjamena said.
The US embassy said its non-essential staff and family members would also be evacuated.
Herve Morin, French defence minister, said France, Chad's former colonial power, which has been accused by the rebels of propping up Deby, would remain "neutral".
But Bernard Kouchner, the French foreign minister, condemned what he called "a brutal attack against an elected and legitimate president".
The US and African Union also condemned the rebels' attack.
The AU has threatened to eject Chad from the 53-nation body if the opposition alliance took power.
The rebels allegedly met little resistance as they advanced across the country from the eastern border with Sudan's Darfur region.
Chad says the rebels are armed and backed by the Sudanese government. Khartoum denies such accusations.