Saturday's earthquake measured 6.2 on the Richter scale and left more than 20,000 injured.

Subandriyo, chief of the Merapi volcanology and monitoring office, said: "The earthquake has caused instability in the lava dome. There is still a chance that a big eruption might occur."

The earthquake brought chaos to the ancient city of Yogyakarta where thousands were trapped when their homes collapsed.

As many as 200,000 people have been made homeless by the disaster, which came two weeks after a smaller eruption from Mount Merapi.

Indonesia is in a zone known as the Pacific Ring of Fire, which is prone to earthquakes and volcanic activity.

Relief efforts planned for another imminent volcanic eruption have been diverted to deal with the quake. UN relief co-ordinator Jan Egeland said the task facing rescue workers, including British aid teams, was enormous.

She said: "Hundreds of thousands will have been affected here. It's a very major disaster, the third one that has hit Indonesia in the last 18 months.

"Hospitals are overwhelmed. It's Day Three after the earthquake and many have severed and crushed limbs, as in all other earthquakes, and it's a race to save their lives."

Many bodies are thought to be trapped and rescuers say the odds of finding survivors are slim.

A major relief operation has begun, with teams from across the country and abroad arriving in the disaster zone. One of Indonesia's most important temple complexes, the ninth century Prambanan Hindu temple, was damaged in the quake. The tremors sent intricate carved reliefs crashing to the ground and destroyed years of restoration work.

United Nations aid agencies are holding talks in Geneva to plan humanitarian relief.