The fighters arrived like a liberating army, greeted by more than 1,000 residents shouting and clapping as their lorries rolled down the streets.

Goma, the largest city in eastern Democratic Republic of the Congo (DRC), had fallen to rebels. M23 fighters captured the seat of the world's biggest peacekeeping operation with ease on Tuesday, parading past UN troops who offered no resistance. Even by the standards of this turbulent region, it was a day of high drama that raised the stakes for further conflict.

M23, allegedly backed by neighbouring Rwanda, marched into the city of 1 million people after the Congolese army crumbled and fled. Scores of heavily armed rebels walked through the city unchallenged as small groups of residents greeted them.

"We are happy, we have been liberated!" said one resident, Pierre Ndjassiang. "We feared a bloody battle but they have taken control quite peacefully. We will work with [M23], and now we will listen more seriously to their demands."

But the crowd streaming around the M23 lorries represented a small fraction of Goma's population, and even some of those present were more circumspect than Ndjassiang.

"We are obliged to welcome M23 but we are not really for or against them," said Lucien Mulire, walking at a distance from the chaotic procession. "There is a very political element to these celebrations. Also, ultimately, people just want an end to hostilities. If that is brought about through victory for the rebels, then people will celebrate. But I would not say they are loved here."

Others said M23's opponents had stayed indoors, fearful of repercussions for dissent.

After nearly eight months of mutinies, skirmishes, advances, retreats, declarations, claims and counter-claims, the actual fighting lasted just a matter of hours. By Monday evening M23, which has been accused of killings, rapes and recruting child soldiers since it launched an uprising in April, had advanced to within four miles of Goma.

On Tuesday morning some bolder civilians crept along the main city boulevard towards the central roundabout where the army and M23 exchanged fire for more than an hour. Volleys of bullets from the rebels' Kalashnikovs whizzed mostly towards army positions, but some flew down the boulevard and prompted those who had crept too close to throw themselves against walls and to the floor. Occasionally the army would respond with heavy arms fire, though that brought only more bullets from the rebels.

In the late morning Gabriel Alamazani, a Congolese non-government organisation worker, appeared on the boulevard, coming from the direction of heavy gunfire.

"There are no more Congolese troops in the town. M23 are here, they have entered the centre of the town, there is no doubt," he said. "I saw over 100 M23 fighters there. Monusco [the UN stabilisation mission in the Congo] is doing nothing; they saw M23 and then left in their trucks."

Within 10 minutes Alamazani was proved right: M23 soldiers marched down Boulevard Kanyamahunga to the Rwandan border and secured the abandoned government buildings there, disarming police as they went. The only government vehicle circulating by the border was, aptly, for the provincial government funeral service.

A crowd of people who had fled to neighbouring Rwanda gathered behind the barrier demarcating the border to watch the rebels assert control. Monusco armoured personnel carriers sped back towards UN bases, less than an hour after having been deployed to the front lines.

Monusco had previously sworn that it would not allow M23 to take Goma, where it has about 1,400 troops; many Congolese were outraged by the UN's inaction. "What purpose do they serve?" demanded one man, who declined to give his name. "They drive out in their tanks, they watch the fighting, then they return. They do nothing!"

A South African Monusco soldier, who did not wish to be named, said: "We [Monusco] have had no trouble with M23, to be honest."

However, a senior UN source, speaking on condition of anonymity, told Reuters: "There is no army left in the town, not a soul ... once they were in the town what could we do? It could have been very serious for the population."

As Goma's civilian population crept back to the streets, many expressed disappointment with the army's failure to defend the city. "We have been let down by the army," said Chantelle Kambeba. "We haven't seen them at all, we don't know where they are."

The city secured, M23 soldiers climbed into trucks and drove through the streets. M23's military leader, Sultani Makenga, was present, though there was no sign or talk of Bosco "The Terminator" Ntaganda, who is sought by the international criminal court for alleged war crimes.

Some in Goma fear that, once international attention is diverted, the rebels will commit abuses that have previously earned condemnation from the UN and human rights groups. Tens of thousands of people have fled neighbouring villages and refugee camps, prompting warnings of a humanitarian catastrophe.

The fight for Goma was less brutal than some feared but did claim innocent victims. In the hot and humid atmosphere of the HEAL Africa hospital, a woman groaned as a bullet was removed from her leg, while a 12-year-old boy, Kakule Elie, had his arm amputated after a bullet smashed the bone.

The hospital's Dr Justin Lussy said two people had been killed and 37 injured by stray bullets or shells. "Many have serious injuries: to the chest and stomach, or bullets which have fractured bones."

The hospital was treating children whose arms were sheared off by exploding shells and teenagers paralysed from the neck down. "There were also three pregnant women who were shot," he said. "Two have lost their children."

Lussy complained of power cuts, staffing shortages and lack of medicine and blood supplies.

Rwanda is accused of equipping M23 with sophisticated arms, including night-vision goggles and 120mm mortars. On Friday the UN group of experts is expected to release its final report, detailing the role Rwanda, and to a lesser extent Uganda, played in the recruitment, financing and arming of the rebel movement.

Lambert Mende, a DRC government spokesman, claimed Rwandan soldiers had crossed into Goma, hiking over footpaths across a volcano that looms between the two countries.

"Goma is in the process of being occupied by Rwanda," Mende, speaking from Congo's distant capital of Kinshasa, told the Associated Press. "We have people who saw the Rwandan army traverse our frontier at the Nyamuragira volcano. They have occupied the airport and they are shooting inside the town. Our army is trying to riposte but this poses an enormous problem for them this is an urban centre where hundreds of thousands of people live."

Rwanda called for an end to hostilities. Louise Mushikiwabo, its foreign minister, said: "What happened today in Goma is a clear indication that the military option has failed to bring about a solution to this crisis and that political dialogue is the only way to resolve the ongoing conflict."

Rwanda denies supporting M23. Mushikiwabo added: "By focusing on the blame game and ignoring the root causes of conflict in the DRC, the international community has missed the opportunity to help the DRC restore peace and security for its citizens and bring about much needed stability in the Great Lakes Region. We just cannot afford to continue along a path that has failed to produce results."

If the rebels succeed in taking another provincial capital, Bukavu, it will mark the biggest gain in rebel territory since at least 2003, when Congo's last war with its neighbours ended.