Military searchers have parachuted down to the wreckage of a Brazilian passenger plane that crashed a day earlier in remote Amazon jungle with 155 people on board.
President Luiz Inacio Lula da Silva said there was no sign of survivors.
The brand-new Boeing 737-800 operated by Brazilian low-cost carrier Gol probably plunged into the ground nose first after it clipped a smaller executive jet, the head of Brazil's airport authority Infraero said.
If the death toll is confirmed, it will be the worst aviation accident in Brazil's history.
Brazil's military suspended the search and rescue mission as dusk set in the thick forested area and will resume it Sunday morning.
"At night in the Amazon you can't see beyond a foot in front of you," said Brigadier Antonio Gomes Leite Filho of Brazil's air force at a news conference.
Earlier in the day, the two soldiers who rappelled from a helicopter into the area were cutting down dense jungle to make a helicopter landing area and authorities had recruited Indian trackers to find a path to the remote jungle crash site for relief teams. Previously, a statement by authorities implied that the soldiers had parachuted into the area.
"All rational logic shows there is a high probability that a collision occurred," Infraero head Brigadier Jose Carlos Pereira told reporters.
The small size of the wreckage area indicated that the chances of survivors among the 149 passengers and six crew members on board were slim.
Gol officials said there were 113 men and 42 women on board, including an 11-month-old boy and four children. The airline said there were only about half a dozen foreigners on the flight, though the company didn't disclose their nationalities.
"Imagine the velocity at which it hit the ground coming from an altitude of 11,000 metres," Pereira told reporters. "It's very unlikely that there will be survivors."
Authorities lost radar contact with Gol flight 1907 on Friday afternoon during its journey from the principal Amazon city of Manaus to the capital Brasilia, the airline said.
Search planes found the crash site in Mato Grosso state, about 1,000km northwest of Brasilia.
Friends and relatives, many wearing dark sunglasses and hugging and crying, gathered on the patio of a hotel in Brasilia waiting for details. Most could not utter more than one word before bursting into tears.
"Gol ... would not say if there might be any survivors," Robson Barreto said as he waited for news on his 29-year-old nephew Rafael who was a passenger.
Denise Abreu, director of civil aviation authority ANAC, said signs indicated there had been a mid-air collision with a smaller jet, which landed safely.
Embraer aircraft manufacturer said one of its executive jets, a Legacy 600 owned and operated by a client, had been involved in a collision and made an emergency landing at Cachimbo air force base with five passengers on board. No injuries were reported.
The Gol plane had been received new from Boeing on September 12 and had only 234 flight hours, the company said.
Until now, the worst air disaster in Brazilian history was the June 1982 crash of a Vasp flight which hit a mountain near Fortaleza in northeastern Brazil, killing 137 people.