The president of Brazil's airport authority, Jose Carlos Pereira, said the newly purchased jetliner may have collided with an executive jet prior to crashing, though that was still under investigation.
If no survivors are found, it would be the worst air disaster in Brazil's history, surpassing the 1982 crash of a Vasp 747 in the northeastern city of Fortaleza that killed 137 people.
Air force helicopter pilots hovering over the crash site saw no signs of an intact fuselage and the debris appeared to cover only a small area. Pereira said the plane apparently hit at nearly 310 mph.
Pereira, said the wreckage was found near the Jarina cattle ranch, 1,090 miles northwest of Sao Paulo in the state of Mato Grosso.
"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 nonexistent," he said.
Pereira said the jungle where the plane crashed is so thick that authorities were planning to use helicopters to lower search and rescue crews by rope to the forest floor. Then those on the ground would cut down trees to create areas large enough for the helicopters to land.
"The jungle is so dense that we're going to have to open it up," Pereira said. "It's a very complex operation, it's extremely humid there, and there are millions of mosquitoes."
The manager of the 49,500 acre ranch said the plane may have crashed inside neighboring the Xingu Indian reservation, a 6.92 million-acre area.
"We heard a loud explosion and some of our employees saw a plane flying low," ranch manager Milton Picalho said by phone. "Judging from the direction the noise came from, I would say it crashed inside the reservation."
Gol airlines Flight 1907 vanished Friday after leaving the jungle city of Manaus en route for Brasilia and Rio de Janeiro.
The flight between Manaus and Rio is popular with foreign tourists but there was no immediate word on the nationalities of those aboard.
The cause of the crash was unclear, but Pereira said the jetliner may have either collided with a Legacy executive jet or the two aircraft may have grazed each other.