The 300-feet-high pile in Meethotamulla had shifted after floods and a fire, and subsequently collapsed on Friday evening, Xinhua news agency reported.
Over 60 houses were damaged with some witnesses saying more than 100 homes were destroyed.
A rescue operation continued overnight following fears many people were buried in the incident.
Several others were admitted to hospital for treatment and over 180 people have been displaced, officials said.
Sri Lanka's President Maithripala Sirisena instructed the Disaster Management Centre to provide assistance to the affected families.
The residents of the area have been protesting over the past several months urging the authorities to move the garbage to another location.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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Doraiah Chowdary Vundavally is a Software engineer at VTech . He is the news editor of SocialNews.XYZ and Freelance writer-contributes Telugu and English Columns on Films, Politics, and Gossips. He is the primary contributor for South Cinema Section of SocialNews.XYZ. His mission is to help to develop SocialNews.XYZ into a News website that has no bias or judgement towards any.