"There is a possibility" of finding survivors, Marival Gomes, Niteroi's civil defence chief, said.
"It's not easy but there is hope."
Firefighters working at the site , however, said there was little chance of finding new survivors after part of the hillside fell away and swallowed everything in its path on Wednesday.
The slum had been built on top of what had been a rubbish landfill site, making the foundations very weak.
The mudslide demolished more than 50 houses as well as churches and stores in its path, leaving a rubble-strewn gash of earth on the hillside.
Marlene Pineiro, a survivor, said she and her family heard a loud noise as the earth began moving and managed to jump out of a window before it collapsed.
"We ran and everything starting coming down ... the kitchen, my brothers' room, the living room," she said.
"But in the other room it stopped, so when that happened we opened the window ... we jumped into the woods and ran away."
About 200 mudslides have hit the Rio area since Monday, triggered by the worst rains in 40 years.
Most of the victims lived in hillside slums, known as favelas, which are usually flimsy structures built on steep hillsides that are susceptible to landslides.
More than a million people live in favelas across the Rio area.
Experts blamed government "complacency" for allowing the country's most destitute to build housing in areas at risk of natural disasters, such as on the sides of steep hills.
But city officials have rebuffed questions about why so many slums were allowed to be built on unstable land, saying the priority is finding survivors and helping to shelter those made homeless.
"This isn't the time to question why these constructions were allowed, it is the time for solidarity," Sergio Cabral, Rio's governor, said as he inspected the disaster zone.
Brazil's federal government has sent troops to help rescue and recovery efforts and on Thursday announced a $113m emergency fund to help Rio state cope with the disaster.