RIO DE JANEIRO (AFP/REUTERS) - As many as 51 people died on Saturday when a passenger bus drove off a cliff in the southern Brazilian state of Santa Catarina, police have said.

Rescue workers were still trying to reach any survivors but access to the crash site in Santa Catarina state was difficult, a local government spokesman told AFP, stressing that the toll could still rise.

The bus, en route from the neighbouring state of Parana, swerved off a curve and fell dozens of metres before crashing in a wooded area. Rescue crews were still trying to rescue survivors and recover the bodies of the victims late in the day.

Initially, police had reported 32 were killed, but later said recovery crews believed an additional 19 were dead. Police did not know how many passengers in all were aboard the bus or whether the driver was one of the victims, but said that at least six survivors were being treated for injuries.

The bus was about 10km from its destination in the city of Joinville when it crashed. Highway and weather conditions at the time were good, a police spokesman said.

Though no immediate cause for the crash had been determined, police said it appeared the brakes on the bus failed.

The tour bus plunged 400m into a wooden ravine as night fell, complicating search efforts, the spokesman said.

The driver is believed to have lost control of the vehicle 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," Colonel Nelson Coelho said in a statement.

Some 43,000 Brazilians are killed in car crashes every year.

And from 2002 to 2012, the traffic accident rate surged by over 24 per cent.

With the economy growing and the population topping 200 million, an estimated 10,000 new cars hit the road every day.