Some 145 homes were destroyed when the 300-foot (90-metre) rubbish mountain came crashing down and police say many more buildings were damaged and could collapse at any time.
Hundreds of soldiers have kept up the search for survivors amid reports that at least six people were still missing after the disaster, which followed heavy rain the previous day and a fire hours earlier.
It came as the country celebrated the traditional new year and followed a warning to Sri Lanka’s parliament that the 23 million tonnes of rotting garbage posed a serious health hazard.
“We are keeping up a search, but we are not very hopeful of finding anyone alive in these conditions,” military spokesman Roshan Seneviratne said on Monday.
Disaster management officials said 1,700 people had been moved to temporary shelters in state schools while the government looked for alternative accommodation.
Prime Minister Ranil Wickremesinghe, who was visiting Japan at the time, said arrangements had been made to remove the garbage dump, but it came crashing down before relocation work could begin.
About 800 tonnes of solid waste from the capital is added to the open dump every day and efforts are under way to generate electricity using the solid waste.
Police have stepped up security in the area following reports of looting and said they arrested 23 men suspected of stealing victims’ belongings.
Wickremesinghe said Japanese Prime Minister Shinzo Abe offered help with the recovery effort and a technical team would be sent to Sri Lanka to evaluate the situation.