Media reports citing a government official say 200 people are feared to be buried.
The state Civil Defense department said the latest slide unleashed by heavy rains hit in Rio's neighboring city of Niteroi. There was no word on how many were missing, but it was feared dozens were buried under the debris.
Although rain let up some late Wednesday, Alves Souza, commander of the firefighters in the Niteroi rescue operations carried out under electric lights, said the work was moving slowly. The wet, steep terrain made it dangerous for anyone trapped in the wreckage and those trying to pull victims out.
"We've managed to recover two bodies and the work is very intense, given the fact that the volume of material we have here is very large," Souza told the Globo television network.
Record rainfall since Monday afternoon triggered deadly mudslides across Rio's metropolitan area, causing at least 147 deaths. At least 60 people were missing, but that didn't include the dozens likely buried under the latest slide that hit Niteroi.
On Wednesday, Rodrigo de Almeira had dug for 15 hours through mud and debris, and he looked like it. Auburn mud covered his head, his ripped shirt, his torn jeans and his rubber sandals.
When asked if he had been able to save anyone from a landslide in the Pleasure Hill slum where he lives, he silently shook his head.
"Right there at least 15 people I know died," Almeira said, staring at a mound of mud and debris. Wood planks - remnants of the shacks engulfed by the surging earth - poked through the mud as 30 rescue workers gingerly dug at it with picks and shovels looking for survivors.
"We found a guy alive this morning, so we had hope," said Almeira, 28. "He didn't make it. We were told he died on his way to the hospital."
Because of the continuing rains, steep hillsides and loose earth, officials said there had been few successful rescues. One man, Carlos Eduardo Silva dos Santos, 24, was pulled alive from under a concrete wall in western Rio. Firefighters said they had no count on how many people had been rescued.
Nearly all the deaths occurred in mudslides that smashed through slums, yet another reminder that life in one of the world's most famous playgrounds is much different for the poor than it is for the rich.
Residents of the shantytowns often endure dangers such as the frequent shootouts between police and heavily armed drug gangs, and when heavy rain falls on slopes crowded with poorly built shacks, nature itself can deal out death.
Almeira and other slum residents say they have nowhere else to go if they want jobs in Rio's richer areas.
"The government wants to forcefully remove the residents living in danger, and that is understandable," said Leandro Ribeiro, another slum resident. "But where are we supposed to go? Some people have been living here for 30 years. This is their home."
Mayor Eduardo Paes said he was taking a tougher stand on forced relocations. He announced that 1,500 families were going to be removed from their homes on Pleasure Hill and in Rocinha, one of Latin America's largest slums.
"I don't want to spend next summer sleepless, worrying if the rains are going to kill somebody," he told reporters, without saying when the relocations would occur.
Rio was in chaos after the record rains this week. Trees and power lines were knocked down, enormous craters were carved in streets, wastewater flowed down to the city's white sand beaches and it was nearly impossible to get anywhere in the city of 6 million people.
In Rocinha, officials said 16 inches of rain had fallen so far this month - three times the amount normally expected for all of April. Similar figures were seen across Rio's metropolitan area.
The Rio state Civil Defense department said at least 11,000 people were forced from their homes. Officials said potential mudslides threatened at least 10,000 houses in the city.
Rio de Janeiro state Gov. Sergio Cabral declared a three-day mourning period, and children were kept from schools Wednesday for a second straight day.