More than 3,000 people have been killed and thousands more injured by a strong earthquake that struck the Indonesian island of Java, officials have said.
The quake, measuring 6.2, flattened buildings in a densely-populated area south of the city of Yogyakarta, near the southern coast of Java.
The Indonesian Red Cross estimates some 200,000 people fled their homes after the quake hit early in the morning.
Electricity and communications across the city were also down, police said.
At least 2,900 people have been seriously injured, and many more are still thought to be trapped under rubble and collapsed buildings.
Indonesian President Susilo Bambang Yudhoyono called on rescuers to work around the clock, as he visited the area with a team of Cabinet ministers on Saturday.
He has also ordered the military to help evacuate victims.
The Indonesian Red Cross said it had sent rapid response teams to the area, and 21 field hospital units were working at full capacity.
The United Nations Secretary General Kofi Annan said a UN disaster response team was ready to help with humanitarian relief, the AFP news agency reported.
Among the many countries promising aid are Malaysia, Japan, Russia and the European Union.
The effects of the quake closed Yogyakarta's airport. Local media said the runway had cracked and part of a roof had caved in.
Yogyakarta is near the Mount Merapi volcano, which threatened to erupt earlier this month, forcing thousands of people to be evacuated.
Experts were divided over whether the quake would affect Merapi, but there are reports of heightened activity at the volcano. There was an eruption soon after the quake which sent debris some 3.5km (2 miles) down its western side.
Officials said that although the area affected was coastal there was no tsunami resulting from the quake.
The quake hit at 0554 local time (2253 GMT Friday), around 25km (15 miles) south of the city of Yogyakarta, the US Geological Survey (USGS) said.
Yogyakarta, Indonesia's ancient royal capital and one of its biggest cities, is about 440km (275 miles) south-east of the capital, Jakarta.
"The earthquake was felt to be massive - larger than the locals here say they've felt in their lives," said Brook Weisman-Ross, regional disaster co-ordinator for Plan International children's charity in Java.
"I was shaken from my bed... As furniture was falling, concrete chunks started falling from my hotel room as people were running out in panic in their bedclothes," he told the BBC.
He said there was extensive damage across the city and that many of the smaller, older houses had collapsed.
But a wide swathe south of the city, in the Bantul and Kulonprogo regions, appears to be the worst hit.
The BBC's Orlando Guzman in Yogyakarta says every other house on the main road south of the city is either flattened or seriously damaged.
Another correspondent in the area, Andrew Harding, says there are a number of dead bodies by the side of the road.
A government official said nearly two thirds of the deaths caused by the earthquake were in Bantul, the Associated Press reported.
Local radio said there were not enough doctors to cope with the numbers of injured.
DEADLY RECENT QUAKES
2005 Muzaffarabad, Kashmir - kills more than 73,000
2004 Asian tsunami, triggered by undersea quake - kills at least 200,000
2003 Bam, Iran - kills 26,271
2001 Gujarat, India - kills more than 20,000
1995 Kobe, Japan - kills 6,430
1999 Izmit and Istanbul, Turkey - kills more than 17,000
1990 Gilan, Iran - kills around 40,000
1976 Tangshan, China - kills 255,000 (official)
People were ferried to hospital in lorries and buses, or made the journey on foot, because of a shortage of ambulances.
Aftershocks have forced medical staff to move injured patients outside.
Orlando Guzman says people here, who have been living in fear of a volcanic eruption for weeks, are very much still on edge. Many are still afraid to go back to their houses.
Mosques, churches and hospitals have been housing people who have fled their homes.
"We're still afraid. We don't want to go home," said Hendra, one of hundreds of people who took refuge at Yogyakarta's Marganingsih Catholic Church.
Indonesia is in a zone known as the Pacific "ring of fire", which is prone to earthquakes and volcanic activity.
In December 2004, a huge earthquake off Indonesia's coast killed hundreds of thousands of people across the Indian Ocean by triggering a tsunami.
Located at borders of several tectonic plates
90% of the world's earthquakes occur along it
Also zone of frequent volcanic activity