A helicopter searching a mountain south of the Indonesian capital has found the wreckage of a Russian Sukhoi plane which disappeared on Wednesday with at least 47 people onboard, the government has said.

The Indonesian military confirmed that the wreckage had been found on Thursday and said teams were working up Mount Salak, a dormant volcano more than 2,100 metres high, Al Jazeera's Step Vaessen reported from Jakarta.

"So far there is no sign of any life on that mountain as far as we know," our correspondent said. "It is still unclear at the moment what caused the crash."

"All we know is that the pilot asked to descend from 10,000 feet to 6,000 feet (3,000 to 1,800 metres) just before they lost contact, so it is a big question as to why the pilot was asking to descend in this mountainous area, and why did the airport tower in Jakarta grant him permission to descend."

Indonesia's president held a press conference earlier, stating a thorough investigation must be carried out into the cause of the crash.

The wreckage was spotted from a helicopter flying over a mountain range in the Bogor district near Jakarta, Mayor Ali Umri Lubis, a member of the military rescue team, told local TV.

Rescuers had resumed their search at first light on Thursday for the plane, which went missing during a demonstration flight early on Wednesday.

The Superjet 100 plane was carrying Indonesian businessmen, Russian embassy officials and journalists. Dimitry Solodov from the embassy said there were eight Russians on board, including pilots and technicians.

"The flight should have lasted just 30 minutes in the area around Jakarta, but it never returned," Vaessen said.

"They [ground control] lost contact after the Russian pilot asked to descend and then they never heard from the plane again.