Indonesia will drop clusters of concrete balls into the mouth of a "mud volcano" in an effort to stop a mud flow that has swallowed villages and left more than 10,000 people homeless since it erupted eight months ago.

On Wednesday the government team handling the crisis will begin lowering chains of concrete balls into the main source of the mud flow, a gas well near Surabaya, in East Java.

The head of the government's technology agency, Said D. Jenie, called the mud flow a natural disaster Tuesday and said the government might need to evacuate more people living near the gas fields, according to the Jakarta Post.

The well erupted May 29, 2006, and has been spewing hot mud since. Estimates suggest as much as 126,000 cubic metres of sediment per day has flowed from the site, displacing more than 10,000 people.

The plan to slow the mud flow with the cement balls is untested and has been controversial since three geophysicists at the Badung Institute of Technology announced it a month ago.

Each of the 1.5-metre-long chains will be connected to two 20-centimetre-diameter and two 40-cm-diameter concrete balls. Each chain assembly will weigh approximately 300 kilograms, and a total of 375 chains with 1,500 concrete balls will eventually be lowered into the main source of the hot mud.

Bagus Nurhandoko, one of the geophysicists behind the plan, told the online journal Nature the aim will be to slow rather than stop the flow of mud.

'Killing the mud softly'

The chains will force the flow of mud around the balls and cause it to lose energy and momentum to friction and vibration, he said.

"It will make the mud tired. We're killing the mud softly," he said.

But critics of the plan said it would do little to slow the flow of mud and might actually increase pressure at the source of the flow, leading to another eruption, or help create another hole from which the mud could escape.

"This is completely [uncharted] territory, nobody has ever done this before," Prof. Richard Davies from Durham University told BBC News. "There is a possibility that the pressure may build, forcing open other vents, possibly exacerbating the situation."

Gas driller implicated

British scientists writing in the February issue of Geological Society of America's GSA Today said the mud flow was "very likely" man made and triggered by commercial gas drilling.

"Once initiated, the fractures would have propagated to the surface, driven by the deep pressure," the report stated.

"It would be highly coincidental for an earthquake-induced fracture to form 200 metres away from this well and provide the entire fracture network required for an eruption on the earth's surface."

Lapindo, the company behind the drilling, disputes that its actions are behind the disaster but has agreed to a government order to pay $488 million (Canadian) to victims and for efforts to stop the mud.

With files from the Associated Press