* Death toll 844, seen as certain to rise
* Three days after quake, full extent of disaster unknown
* President Widodo promises food, supplies
* Disaster agency says more equipment, personnel needed
* Red Cross report deaths of 34 children at Christian camp (Updates with comment from survivor, minister on IMF meeting, adds detail, bylines)
By Fathin Ungku and Kanupriya Kapoor
PALU, Indonesia, Oct 1 (Reuters) - Indonesian authorities scrambled on Monday to get help into quake-hit Sulawesi island as survivors streamed away from their ruined homes and accounts of devastation filtered out of remote areas, including the death of 34 children at a Christian camp.
The confirmed death toll of 844 was certain to rise as rescuers reached devastated outlying communities hit on Friday by a 7.5 magnitude earthquake and subsequent tsunami waves as high as six metres (20 feet).
Dozens of people were reported to be trapped in the rubble of several hotels and a mall in the small city of Palu, 1,500 km (930 miles) northeast of Jakarta. Hundreds more were feared buried in landslides that engulfed villages.
Of particular concern is Donggala, a region of 300,000 people north of Palu and close to the epicentre of the quake, and two other districts, where communication had been cut off.
The four districts have a combined population of about 1.4 million.
President Joko Widodo told reporters getting those people out was a priority.
"The evacuation is not finished yet. There are many places where the evacuation couldn't be done because of the absence of heavy equipment, but last night equipment started to arrive," Widodo said.
"We'll send as much food supplies as possible today with Hercules planes, directly from Jakarta," he said, referring to C-130 military transport aircraft.
The disaster agency said later more heavy equipment and personnel were needed to recover bodies.
MASS GRAVE
One woman was recovered alive from ruins overnight in the Palu neighbourhood of Balaroa, where about 1,700 houses were swallowed up when the earthquake caused soil to liquefy, the national rescue agency said.
"We don't know how many victims could be buried there, it's estimated hundreds," said Sutopo Purwo Nugroho, spokesman for the National Disaster Mitigation Agency.
All but 23 of the confirmed deaths were in Palu, a city of about 380,000 people, where workers were preparing a mass grave to bury the dead as soon as they were identified.
However, nearly three days after the quake, the extent of the disaster was not known with authorities bracing for the toll to climb - perhaps into the thousands - as connections with remote areas up and down the coast are restored.
Aid worker Lian Gogali, who had reached Donggala district by motorcycle, said hundreds of people facing a lack of food and medicine were trying to get out, but evacuation teams had yet to arrive and roads were blocked.
"It's devastating," she told Reuters by text.
Indonesian Red Cross spokeswoman Aulia Arriani said a church in an area of Sigi district, south of Palu, had been engulfed in mud and debris. Officials said the area suffered liquefaction, when the shock of the quake temporarily destabilises the soil.
"My volunteers found 34 bodies ... children who had been doing a bible camp," Arriani said.
Sulawesi is one of the earthquake-prone archipelago nation's five main islands and sits astride fault lines. Numerous aftershocks have rattled the region.
Pictures showed expanses of splintered wood, washed-up cars and trees mashed together, with rooftops and roads split asunder. Access to many areas is being hampered by damaged roads, landslides and collapsed bridges.
THREATS OF VIOLENCE
A Reuters witness said queues at petrol stations on the approaches to Palu stretched for kilometres. Convoys carrying food, water and fuel awaited police escorts to prevent pilfering before heading towards the city while residents streamed out.
One aid worker spoke of threats of violence among survivors seeking fuel.
The state energy company said it was airlifting in 4,000 litres of fuel, while Indonesia's logistics agency said it would send hundreds of tonnes of rice. The government has allocated 560 billion rupiah ($37.58 million) for the recovery.
Military aircraft were taking people out of Palu and hundreds of people thronged its small airport as officers struggled to keep order.
"I'd get a plane anywhere. I've been waiting for two days. Haven't eaten, barely had a drink of water," said 44-year-old food vendor Wiwid.
Indonesia, which is on the seismically active Pacific Ring of Fire, is all too familiar with earthquakes and tsunamis. A quake in 2004 triggered a tsunami across the Indian Ocean that killed 226,000 people in 13 countries, including more than 120,000 in Indonesia.
Questions are sure to be asked why warning systems set up after that disaster appear to have failed on Friday, and why more people in coastal areas had not moved to higher ground after a big quake, even in the absence of an official warning.
Disaster agency spokesman Nugroho told reporters on Sunday none of Indonesia's tsunami buoys, one device used to detect waves, had been operating since 2012. He blamed a lack of funds.
The meteorological and geophysics agency BMKG issued a tsunami warning after the quake but lifted it 34 minutes later, drawing criticism it had been too hasty.
However, officials estimated the waves had hit while the warning was in force.
Indonesia had assured the International Monetary Fund and World Bank is could host their meeting on Bali island this month, government minister Luhut Binsar Pandjaitan said in a statement.
"We are always ready. We have showed them that Indonesia is able to deal with even the most difficult circumstances."
(Additional reporting by Reuters stringer in PALU, Fergus Jensen, Fanny Potkin, Tabita Diela, Agustinus Beo Da Costa, Gayatri Suroyo and Fransiska Nangoy in JAKARTA Writing by Robert Birsel Editing by Paul Tait and Nick Macfie)
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