Among the dead were eight children and 24 women, regional government spokeswoman Ana Paula Keller said.
The toll had initially been put at about 30 but the number rose throughout the night as rescuers continued to find bodies at the difficult-to-access crash site in Santa Catarina state, and other victims succumbed to their injuries at a nearby hospital.
The bus plunged 400 meters (1,300 feet) into a ravine and ended up on its side, snarled in thick vegetation. Rescuers struggled to account for everyone in the failing light and difficult terrain.
Fifty people were supposed to be on the bus, but authorities believed the number of passengers was higher than that.
Ten people were in the hospital. Their conditions were not immediately known.The crash site was near a lookout point in the Dona Francisca mountains, a popular stop for tourists. The bus was operated by a tour firm and was traveling a route of about 300 kilometers (185 miles) between Uniao da Vitoria and Guaratuba, on the Santa Catarina coast.
Witnesses told local press that the driver lost control on the curvy stretch of highway, but the cause was still under investigation.
"There are people out there, on the hill, in the bus, trapped in the wreckage. But the chances of finding someone alive are pretty slim," state police Colonel Nelson Coelho said in a statement.
Several people stopped on the roadside to try to help victims as they waited for emergency services to arrive.

Accidents on this winding road are common. The local newspaper said 66 people had been killed on the highway in the last five years. In 2007, 27 people were killed in a single accident and another crash in 1999 left 35 dead.

Some 43,000 Brazilians are killed in road accidents annually.And from 2002-2012, the traffic accident rate surged by over 24 percent.
With the economy growing and the population topping 200 million, an estimated 10,000 new cars are added to the roads every day.
One of the country's last major accidents was in October 2014, when a truck collided with a bus carrying high school students in Sao Paulo, killing 10 and injuring dozens more.

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