AT least 112 people have been confirmed dead after a river overflowed triggering an avalanche of mud and water that swept through a Colombian city.

Families were swept away as they slept as the violent torrent crushed buildings and devastated neighbourhoods in the early hours of Saturday. Hours of heavy rains overnight caused rivers to burst their banks, flooding homes with mud in Putumayo province.

Muddy water and debris surged swiftly through the city of Mocoa's streets, burying whole neighbourhoods, toppling homes, ripping trees from their roots, lifting cars and lorries and carrying them downstream.

With most of the community in the Putumayo region asleep when the water avalanche began, many residents did not have enough time to climb on top of their roofs or seek safety on higher ground.

The region, bordering Ecuador and Peru, is heavily dependent on agriculture and the petroleum industry.

Herman Granados, a surgeon at the city's hospital, said he believed there is likely to be more than 300 people injured and that doctors were quickly running out of blood and other critical supplies.

He suspected the death toll would rise, saying: "Under the mud, I am sure there are many more."

Medics worked throughout the night on patients.

President Juan Manuel Santos visited the region and as the military and disaster authorities mobilised to respond to the disaster. He said in a statement: "Our prayers are with the victims."

Witnesses described feeling buildings vibrate as the flood began.

Although an alarm reportedly went off, it could not be heard throughout the city, survivors said.

Videos that some residents posted online showed vast areas filled with wood planks and debris. People could be heard calling out the names of missing loved ones.

Oscar Forero, a spokesman for the Colombian Red Cross, said: "There are many people looking for their relatives."

The Red Cross was setting up a special unit in Mocoa on Saturday afternoon to help relatives search for their relatives.

President Santos also warned the death toll would rise even further as the search for survivors continues at the disaster zone.

Mocoa is a city of 50,000.While landslides and heavy rains are common in the mountainous area, March was Colombia's rainiest month since 2011, according to the state meteorological agency.

In neighbouring Peru, more than 90 people have died since the start of the year because of unusually heavy rainfall, which also caused landslides and flash floods.

Meteorologists across Colombia are on alert because this year’s rainy season is combined with La Nina, which is a phase of the weather phenomenon El Nino, bringing extra rain from the Pacific Ocean.

In Mocoa, the excess in rainfall caused the overnight overflowing of three rivers, the Mocoa, the Mulato and the Sancoyaco.

The floods caused an avalanche of mud and bricks that wiped away “much of the city” shortly after midnight, Mocoa Mayor Jose Antonio Castro was quoted as saying by newspaper El Tiempo. Rescue services said 17 neighbourhoods had been affected and Castro said his own house had also been destroyed.

"The mud is up to the roof," he told Caracol radio.

Two bridges were also swept away, he said.

Castro also said hospitals urgently need medicine and surgical equipment to attend to the victims.

The Putumayo region is known for its picturesque waterfalls and lagoons and is popular with backpackers and trekkers.