Eight passengers survived the crash, Emergency Minister S. Otgonbayar said, adding that some of the trapped passengers would need to be cut out of the helicopters' mangled wreckage.
"Doctors and nurses have been sent to the crash site to give assistance and a rescue team is working at the site," Otgonbayar said.
The crash site was found Saturday after authorities lost contact with the Russian-made Mi-8 helicopter on Wednesday Otgonbayar said.
The helicopter crashed into a mountain, making rescue work difficult, he told reporters. The dead included two of the three pilots on board.
The helicopter had been taking firefighters and equipment to a forest fire in Selenge province when it disappeared from radar screens Wednesday, Otgonbayar said.
Relatives of the victims complained to reporters that the government did not mount a search for the helicopter until Friday, and that officials initially reported that the helicopter had landed safely after running short of fuel.
"My brother survived, but we want to know why they did not immediately start rescue operations after they lost contact with the helicopter," one man, who uses just a single name, Ganholog, said to reporters.
No other details were immediately available.
The helicopter belonged to the Mongolia's Defense Ministry.