More and more teams are arriving in Padang to aid relief work
International aid is starting to arrive in Sumatra as concern grows that remote areas may have been devastated by Wednesday's powerful earthquake.
British, Australian and South Korean rescuers have arrived and the EU and Russia are also sending help.
More than 1,000 people are known to have died and up to 3,000 more are believed trapped beneath collapsed buildings in the city of Padang.
Widespread destruction has also been reported in surrounding areas.
Red Cross officials say remote village areas outside Padang appear to suffered severe and widespread damage, and in some cases have been completely destroyed.
"We also need drinking water and clothes because many people's clothes were burnt in fires," one Red Cross worker, Testos, told Reuters news agency.
"We also need medicines to stop infection."
But access to these areas remains difficult, and few details are known yet of the extent of the destruction or the loss of life.
Local TV stations have begun to reach some of the affected areas, broadcasting images of villages reduced to rubble and tales of villagers without access to clean water.
"We have not received a thing. We need food, clothes, blankets, milk. It seems like the government has forgotten about us," Reuters quoted one woman, Siti Armaini, as saying in Pariaman, 40km (25 miles) north of Padang.
In Padang, witnesses report that the stench of decomposing bodies now hangs over collapsed buildings as rescuers battle to reach survivors.
Many buildings in Padang simply could not withstand the shaking
Food shortages are being reported in areas where the earthquake has damaged roads, while people who lost their homes are said to be sleeping in the streets.
At the collapsed wreckage of a hotel, rescuers were working frantically throughout Saturday to find any of eight people thought to have survived Wednesday's earthquake.
One person trapped in the ruins of the Ambacang Hotel sent a text message to a relative on Friday asking for help, rescuers revealed.
The text message reportedly implored rescuers: "Be careful that the excavator doesn't cause the building to collapse on us."
Those trapped are believed to be on what was the 6th floor and rescue teams have been building a tunnel through the rubble to reach them.
But by mid-afternoon in Padang none of the eight had been located.
The BBC's Alastair Leithead, who is in Padang, says that as the hours pass, the rescue operation is turning into the recovery of bodies.
Specialist teams from around the world have begun arriving at co-ordination centres in Padang, waiting to be deployed to the field.
The Red Cross planned to hold a meeting in the city on Saturday to co-ordinate relief efforts.
The priority is to ensure injured survivors receive the medical attention they needed, Red Cross officials say.
Two Australian planes carrying medical personnel and rescue experts have arrived in Padang, with dozens of British firefighters due to join a 16-man deployment late on Saturday.
A Swiss sniffer-dog team is already on the ground, and Russian, Estonian and Japanese personnel have all been sent. Countries around the world have pledged relief funds.
Indonesian President Susilo Bambang Yudhoyono has also called for $10m (£6.2m) in government aid to be distributed quickly.
"The... fund has to flow quickly, no more bureaucracy for this," he said. "This is an emergency, so speed is crucial."
Wednesday's 7.6-magnitude quake struck off the coast of Padang and caused devastation. A second quake of 6.8 struck nearby on Thursday causing panic but no reports of damage or casualties.
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