The task of helping survivors of Saturday's earthquake on the Indonesian island of Java is "a race against the clock", the United Nations has warned.
Emergency workers and supplies are arriving but the UN's top relief co-ordinator Jan Egeland told the BBC the task was "enormous".
Driving rain is hampering relief work after the disaster which killed at least 4,295 people and injured 20,000.
And activity at nearby erupting volcano Mount Merapi is said to have increased.
UN aid agencies meeting in Geneva say field hospitals, shelter, medicines and clean water are the top priorities after the 6.3 quake which struck on Saturday morning.
OFFERS OF AID
Japan: $10m (£5.4m) plus troops
UK: $5.5m via UN, $1.8m via Red Cross
Middle East: $13m in total from Saudi Arabia, UAE and Kuwait
Pledges from EU, US and China
Appeals by Red Cross, Save the Children
They want to make sure the operation gets under way quickly and efficiently and that there is no duplication, the BBC's Imogen Foulkes reports.
The UN appealed for three field hospitals to be sent to the region within three days.
Among other measures being taken:
- The Red Cross is sending 10,000 tents and Unicef is supplying school tents
- A UN co-ordination centre has been set up at Yogyakarta Airport, close to the disaster zone
- The World Food Programme has begun giving out emergency rations and Unicef is distributing 40,000 litres of clean water a day
Many aid agencies already have supplies in the region because of the threatened volcanic eruption, our correspondent notes.
Buildings in and around Yogyakarta were flattened in the earthquake, leaving about 130,000 people homeless, according to Unicef.
Heavy rain has forced some to return to their destroyed houses in search of some kind of shelter despite the threat of further building collapses.
The quake probably affected "hundreds of thousands", Mr Egeland told the BBC's World Today programme.
In an interview with CNN, the UN relief co-ordinator added that he expected relief to reach people faster than after the 2004 tsunami disaster, which killed at least 130,000 in the western province of Aceh.
"This time I think it's going to be easier because Java is not as remote as Aceh," he said.
Governors of the areas hit by the quake have put the death toll at 4,295 in contrast to earlier estimates of about 5,000.
Many bodies are still thought to be trapped under debris and rescuers say the odds of finding survivors are slim.
Some two-thirds of the victims died in Bantul, a town south of the ancient royal city of Yogyakarta.
Aid agencies and the military are working together to get aid to surrounding towns and villages.
Hospitals are overwhelmed and hundreds of victims are having to be treated outdoors.
One BBC News website reader in Yogyakarta, Kirsty, said she had visited a hospital and witnessed operations being performed "on the floor, atop bamboo mats or mattresses".
Thousands of people have been evacuated from around Mount Merapi, close to Yogyakarta, where volcanologists report a three-fold increase in activity since the quake.
Columns crashed to the ground at the Prambanan temple
Subandriyo, chief of the Merapi volcanology and monitoring office, said there was a chance of a "big eruption".
Indonesia is in a zone known as the Pacific Ring of Fire, which is prone to earthquakes and volcanic activity.
Yogyakarta is the former Javanese royal capital and home to historic temples and palaces.
Intricate carved reliefs in its renowned Prambanan Hindu temple were sent crashing to the ground by the quake, which undid years of restoration.
However, the 7th Century Borobudur Buddhist temple survived intact.
Located at borders of several tectonic plates
90% of the world's earthquakes occur along it
Also zone of frequent volcanic activity