Brazilian President Luis Inacio Lula da Silva has declared three days of national mourning after the crash of a passenger plane with 155 people aboard.
Relatives gathered at airports in Brasilia, Rio de Janeiro and Manaus
There is no sign of survivors at the crash site in the Amazonian state of Mato Grosso, the air force said.
Soldiers dropped into the remote area have been clearing dense vegetation so that helicopters can land.
The Boeing 737 was flying from Manaus to the capital, Brasilia, when it vanished from radar screens on Friday.
Aviation officials are investigating the possibility that it collided with a smaller plane.
If no survivors are found, Friday's crash would become the worst air disaster in Brazil's history.
The plane was operated by the budget airline Gol.
"It would be very difficult for anyone to survive such a crash," Jose Carlos Pereira, president of the Brazilian airport authority, told journalists.
"Our experience shows that when one cannot find the fuselage relatively intact and when the wreckage is concentrated in a relatively small area, the chances of finding any survivors are practically non-existent," he added.
However, authorities say they have not given up hope and will continue a search of the site at first light on Sunday.
A Gol airline statement state said the wreckage had been found 30 km (19 miles) north of the town of Peixoto Azevedo.
BRAZIL'S GOL AIRLINE
The low-cost Brazilian airline was founded in 2001
It is modelled on the British budget airline Easyjet
It had a fleet of 55 aircraft prior to the accident
The airline had not suffered a crash before
Gol is expected to have more than 100 aircraft by the year 2012
It took rescuers more than 20 hours to reach the site.
Dozens of anxious relatives and friends of those missing have gathered at airports in Brasilia, Rio de Janeiro and Manaus, seeking information about their loved ones.
Initial reports said the airliner collided with a smaller private plane, but aviation officials now say this cannot be confirmed.
It had been scheduled to fly on to Rio de Janeiro from Brasilia.
Gol has expanded rapidly in recent years to become Brazil's number two carrier.
This is the first major crash involving Gol, which was founded in 2001.
Gol says the plane involved was new, having come into service this month.