"Today we reached the crash site... and we found 12 victims and they were all dead. We will continue the evacuation process," said Daryatmo, head of the national search and rescue agency, who goes by one name.
"I still don't know the condition of the bodies, but we haven't been able to evacuate them. The bodies are still in body bags," he told reporters in Jakarta.
Daryatmo said that rescuers arrived at the difficult-to-reach, jungle site on the sheer face of Mount Salak, where the Sukhoi Superjet 100 slammed into the dormant volcano south of Jakarta, by foot and helicopter.
Crews used climbing equipment including ropes to ascend the near-vertical mountain face, authorities said.
Helicopters had been trying to reach the site since a chopper spotted the wreckage Thursday, but had been hampered by thick fog, according to authorities.
All aboard the flight were killed, authorities said Thursday, a day after the plane crashed during a demonstration flight that was meant to spur international sales of Russia's first post-Soviet civilian jet.
The company representing Sukhoi in Indonesia, Trimarga Rekatama, originally said 50 people were on board but Thursday revised the number to 45. Local rescue officials said the plane was carrying 46 people.
Those aboard were mostly Indonesian aviation representatives, but there were also eight Russians -- four of them crew and four Sukhoi employees -- plus an American and a Frenchman, officials said.