The number of dead is expected to rise further as some 30 people, or maybe more, are still feared trapped under the rubble, Xinhua reported, citing police sources.
The victims include three rescue workers, said media reports, adding that 38 others were injured during the mishap.
The supermarket, built in 2011, belongs to the Lithuanian-owned Maxima chain, the second largest retailer in the country.
Rescue work is proceeding slowly as both the rubble and remaining sections of roof are at risk of further collapse.
The reason for the collapse is currently unknown, but reports said a garden with trees and plants was being built on the store's sizeable roof, which might have violated construction regulations and triggered the collapse.
Rescue officials are unsure about the number of survivors under the rubble, but expect that the death toll will rise.
The government has announced three days of mourning from Saturday.