Survivors of Java’s earthquake fled in panic today when huge clouds of scalding gas were expelled from Mount Merapi, Indonesia’s most active volcano.

Families packed onto mopeds to abandon their homes and pour down the mountain side, after a series of deafening explosions heralded the gas clouds at about 9am local time.

Many believed that it was the start of Merapi’s long feared full eruption. Many of those who fled were still traumatised after the earthquake on May 27 which killed 6,000 in the area south of the volcano.

Today's deadly gas clouds known as pyroclastic flows, which reach temperatures of 800C incinerating everything in their path, were the biggest since the volcano became active last month.

One of 20 clouds travelled three miles scorching an area of forest and stopping just short of a settlement. Thirty-three lava flows were counted.

Volcanologists fear that the earthquake, which measured 6.3 on the Richter scale, destabilised the lava dome in the volcano's cone. If it gives way, rivers of molten magna may flow into villages at the cone's base.

Pyroclastic flows are also a great danger on Merapi. Sixty villagers were burned alive in 1994 by one in the volcano’s last major eruption.

Around 23,000 villagers have left their homes in the last few days, many evacuating for the second time after a scare on May 15 when eruption was believed to be imminent.

A few have stayed in their homes to protect them from looters. "Of course we’re worried," one villager called Supriatun said. "But as long the hot clouds do not reach us we won’t leave our village."

Just a handful of tough farmers, village security men, and curious sightseers were left last night at Kinahrejo, the last settlement before the volcano.

One man, Sunadi, 24 said: "Luckily the earthquake didn’t kill anyone here but we really fear Merapi. But when people saw the clouds they really panicked and there was a big rush downhill."

Three miles away, great rivers of molten lava were flowing down the steep cone. The few remaining men were using walkie-talkies to warn each other about pyroclastic flows.

A few miles downhill hundreds of villagers had gathered at a government evacuation station.

Ati Sehono, a grandmother in her 70s had escaped Kinahrejo in the morning in a truck with her family. "We were very scared," she said. "But in my life I have had to escape Merapi five or six times already."

Aid groups which have been busy helping more than half a million people made homeless by the earthquake are now preparing for a second disaster. Oxfam is among those drawing up plans to assist hospitals and emergency services already severely stretched by the earthquake.

Oxfam has 10,000 tarpaulins ready to distribute, as well as special kits to help villagers cope with an eruption, containing binoculars, loud hailers and flashlights.

Times Recommends

• A doctor, a daughter and a man called Johnny
• Mona Lisa's smile may belie ill health
• ‘Parasite economy’ lies behind Greek tragedy