Homes, people and livestock were engulfed by the landslide at a vast landfill site in the capital, Kampala.
After torrential rain in recent weeks, a chunk of rubbish from the city’s only landfill site broke off late on Friday, crushing and burying homes on the edge of the site as residents slept.
On Saturday, the Kampala Capital City Authority had put the death toll at eight.
“The latest we have is 13 dead, but rescue services are continuing,” police spokesman Patrick Onyango said on Sunday.
At least 14 people have been rescued so far, he said, adding that more could still be trapped but the number is unknown.
Tents have been set up nearby for those displaced by the landslide, the Uganda Red Cross Society said.
The landfill site, known as Kiteezi, has served as Kampala’s sole rubbish dump for decades and had turned into a big hill.
Residents have long complained of hazardous waste polluting the environment and posing a danger to residents.
Efforts by the city authority to procure a new landfill site have dragged on for years.