It is estimated than 200,000 peope are in need of urgent humanitarian assistance after a tidal wave travelling at 400 mph was unleashed by the earthquake on September 28.
The death toll of 1,500 is rising by the day - but fear is now mounting for those who survived.
“A 400 mile-an-hour tsunami also kills slowly,” spokesman for the Disasters Emergency Committee DEC said.
DEC is co-ordinating the fundraising appeal on behalf of 14 leading aid agencies and charities working in the stricken region.
Palu City has been ripped apart by the natural disaster with agencies to attempt to reach 25 villages in Donggalla regency in the north of the island over the weekend.
So far, people there have been cut off from help with it feared up to 1,000 villages have either been wiped out or severely damaged across the island.
Aid agencies have so-far been hampered by lack of electricity and fuel in the stricken region.
In the city of Palu alone, more than 71,000 people are sleeping on the streets, in gardens, in paddy fields and on football pitches after losing their homes, many which were submerged when the earthquake caused the ground to liquify.
Some are simply too scared to return to their properties for fear of aftershocks and further tremors with families clustered together in the open-air.
Many children remain separated from their parents with reports of young ones turning up to hospitals alone. A number of hospitals have been destroyed with those that still stand overwhelmed as medical supplies run low.
More than 100 people are still unaccounted but hopes of finding more survivors fade by the hour.
Wayhu Widayanto , Emergency Preparedness and Response Manager with Care International, said the priority was to get food, basic hygiene packs and shelter kits to the people.
Speaking from Palu City, which now has limited electricity supply, he said: “We need to move quickly to purchase, provide and distribute these items before rainy season. We can’t wait for a month to get these items.
“It is very good there is no rain at the moment. I can’t imagine what it will be like when the rain starts.”
An emergency shelter kit for a family, which contains a tarpaulin or tent and blankets costs £30.
A basic hygiene kit, which includes a 12-litres bucket, soap, detergent and sanitary items, costs a fraction of that.
Just £50 could feed a family for a month, DEC said.
Mr Widayanto said that ready-to-eat rations were expected to become an urgent humanitarian need in the coming days.
Provisions of rice and noodles are reaching some of those affected but damage to roads and limited air traffic capabilities is slowing distribution.
Some have gone without food for several days, with shops looted for supplies as desperation mounts.
Another key concern is drinking water. As pipes ruptured in the quake, water supplies have become contaminated with purification tablets urgently sought. Without fuel to run generators, the ability to boil water is lost.
Fear and grief mix on the streets as the aftermath of the quake and tsunami, which sent waves towering up to 18 feet across the island, becomes impossible to bear.
Fake news spreads hoax messages about further earthquakes with the Indonesian Government involved in a counter operation to spread accurate information to the people.
Mr Widanyanto said: “People are scared. In Palu, people are queuing up to get petrol from 7am and waiting until 3pm to get it. People want to leave.”
With roads impassable in places - an the threat of landslides high - further major challenges lie ahead for those wanting to flee.
The Disasters Emergency Committee (DEC) appeal on behalf of survivors of the tsunami and earthquake has raised more than £6 million since it launched on October 4.
The UK Government matched pound for pound the first £2 million donated by the public to the DEC Indonesia Tsunami Appeal with the Scottish Government adding £240,000 this weekend.
DEC Chief Executive Saleh Saeed said: “The situation in Indonesia remains desperate and hundreds of thousands of people urgently need food, clean water, shelter as well as support in dealing with the trauma they have experienced. As the full impact of the disaster unfolds, DEC member charities and their partners are ready to help devastated communities to rebuild their lives.
“We would urge people to continue donating. Please donate now.”
Donations can be made on the DEC website at dec.org.uk or by phone on 0370 60 60 900
Donations of £5 can be sent by texting SUPPORT to 70000
Alternatively, send donations to DEC Indonesia Tsunami Appeal,PO Box 999,London, EC3A 3AA