Bogota: Some 100 children were among the 311 people killed in the giant mudslide that slammed into the southern Colombian town of Mocoa last week, the government has said.

The mudslide hit late Friday after heavy rains caused three rivers to flood, sending a sea of mud, boulders and debris crashing into the town.

The latest death toll was given by the country's Disasters Risk Management office. More than 300 people remain missing, according to President Juan Manuel Santos.

Mocoa, the capital of the department of Putumayo, was home to 70,000 people, about 45,000 of whom were affected by the disaster, according to the Red Cross.

In an effort to speed up reconstruction, the government formally declared a 30-day state of economic, social and ecological emergency in Mocoa, which will allow direct contracting of services without the need for formal, more time-consuming procedures.

The hardest-hit areas were impoverished neighbourhoods populated with residents uprooted during Colombia's five-decade civil war.

Authorities are investigating whether local and regional officials correctly enforced building codes and planned adequately for natural disasters.

The mayor, the governor and their predecessors are also being probed to see whether they bear any responsibility, according to Colombian media reports. The mudslide turned Mocoa into a wasteland of earth, boulders and debris.

Many survivors have had to take the disaster response effort into their own hands, clawing through the mud for their loved ones, digging their graves themselves and defending what belongings they have left from looters.