Forty nine high school girls died in the inferno after their bus was crushed between two vehicles on Wednesday.
The accident happened on a dark, busy highway near Situbondo, 830 km east of Jakarta.
The students were returning from a field trip on the resort island of Bali when their bus was hit by an oncoming truck, then rammed from behind by another vehicle.
"They were all mostly charred as the bus they were on caught fire in the accident," police spokesman Supoyo said.
Flames and thick smoke quickly engulfed the vehicle causing panic, bus driver Arwandu told police.
"We can certainly say that in term of numbers of victims, this is the most serious traffic accident that has taken place in the country this year"
Second Brigadier Kusmiarni
"I had the time to instruct the children to open the back door, but it turned out they could not.
Despite the pains that I got from being thrown in the collision, I broke some windows but the fire spread too fast," he said.
Wrecks of the bus and the two other vehicles involved were still burning three hours after the accident, witnesses said.
The bus was the last of three vehicles which had been transporting students from a three-day field trip on Bali to the Yapenka I high school near the city of Yogyakarta.
Its driver escaped with light injuries while his assistant suffered burns.
The driver of the truck fled and is now being sought by the police while his assistant is currently under questioning, Supoyo said
"We can certainly say that in term of numbers of victims, this is the most serious traffic accident that has taken place in the country this year," said police Second Brigadier Kusmiarni.
Supoyo added that investigators suspected the brakes of the truck had malfunctioned, causing it to veer into the opposite lane while speeding on a downward sloping road.
At the general hospital in Situbondo, burned bodies were laid out on plastic sheeting to be examined by reinforcement medics drafted in from neighbouring towns.
The students were returning from
a field trip in Bali
Meanwhile, a team of 10 officials from the girls' home town of Sleman were dispatched to Situbondo on Thursday to help organise the return of the deceased and injured and liase with the victims' families.
Sleman district police chief, Sigit, said he would accompany two bus loads of victims' relatives to Situbondo later on Thursday to help identify bodies.
Traffic jams stretched up to 14 km long as police diverted traffic, creating a three hour detour to allow ambulances to get to the scene.
Indonesia's hazardous roads are responsible for 29 accidental deaths a day, with an annual toll of 10,500, according to police statistics.