LONDON - The collapse of the world's fastest-growing mud volcano could redirect nearby rivers and threaten villages in Indonesia, researchers said on Wednesday.

The central part of the volcano on the island of Java is collapsing at a rate of up to three meters a day sporadically, they reported in the journal Environmental Geology.

"Sidoarjo is a populated region and is collapsing as a result of the birth and growth of Lusi," Richard Davies, a geologist at Britain's University of Durham.

"This could continue to have a significant environmental impact on the surrounding area for years to come."

Villages on the outside of the mud volcano now covering seven square kilometers may be at risk in coming years, the British and Indonesian researchers said.

Thousands of homes and factories have already been submerged by the hot mud since it first started to erupt in May 2006, displacing an estimated 30,000 people.

A mud volcano is usually a naturally occurring phenomenon created when a mix of mud, water and gas forms underground and is forced to the surface. There are few thousand on earth.

Scientists say the mudflow in the Sidoarjo region, near the country's second biggest city, Surabaya, was caused by a gas drilling operation by PT Lapindo Brantas.

Lapindo and PT Energi Mega Persada Tbk, which has a stake in Lapindo, dispute that drilling caused the disaster, which started two days after a large earthquake in Central Java.

Using GPS and satellite data recorded between June 2006 and September 2007, the researchers showed the area affected by Lusi has disappeared into the ground at a rate of 0.5 meters per year on the outer edges and 14.5 meters in the centre.

"This is the first time the measurements have been taken, recorded and published," said Davies who worked on the study.

The researchers, led by Hasan Abidin of the Institute of Technology Bandung in Indonesia, calculate that if the volcano continues to erupt for three to 10 years at the constant rates measured during 2007 then the central part could collapse by as much as 146 meters.

"If we establish how long the volcano will continue to erupt then the ... data will allow us to assess the area that will ultimately be affected by this disaster," Davies said.