Indonesian rescuers on Sunday flew to the jungles of Borneo island to bring back the bodies of 13 people killed when an army helicopter crashed and burst into flames a day earlier.

Six people were also injured when the aircraft, carrying construction workers to build a military outpost, smashed into a cliff as it tried to land at the remote site near the Malaysian border.

The start of the mission to retrieve the bodies was delayed for several hours Sunday by bad weather but clouds cleared later, allowing a helicopter to fly to the remote area.

It was carrying mountaineering equipment so that rescuers -- mainly military and search and rescue agency personnel -- could reach the wreckage on a cliffside in Malinau district in North Kalimantan province.

Rescuers quickly found 11 of the 13 bodies in the helicopter, which had been reduced to a charred wreck, and put them in body bags, military spokesman Legowo Jatmiko told AFP.

"It's bright and sunny now and rescuers said they did not face much of a problem. We believe we will be able to evacuate all the bodies today and airlift them" to Tarakan, a town in northern Borneo, he added.

Three other aircraft were on standby to help if needed.

President Susilo Bambang Yudhoyono expressed his "deep sorrow" at the deaths.

"Hopefully the families of the soldiers and other victims will find fortitude in the face of this tragedy," he said in a tweet.

Jatmiko said rescuers must also retrieve the black box flight data recorders from the Russian-made Mi-17 aircraft, which was completely burnt out following the accident.

Once the bodies have been evacuated, an investigation into the cause of the crash will begin.

Military officials said they suspect it was caused both by bad weather and a problem with the back rotor blades, which appeared to spin out of control just before the helicopter hit the cliff.

Eight of those killed were civilian construction workers and five were crew members, who were military personnel. The six survivors were still in hospital receiving treatment for burns.

Borneo is a vast island shared between Indonesia, Malaysia and Brunei, covered in lush jungle and home to rare animals such as orangutans.

There have been numerous fatal air crashes over the years in Indonesia and some have involved military aircraft.