"Concrete balls fail to stem mud flow in Indonesia"

A plan to drop concrete balls into an oozing Indonesian "mud volcano" to slow its disastrous flow may be revised after they slid far deeper than expected.

The balls fell one kilometre into the crater, about twice the depth anticipated, so more may be required to staunch the mudflow, according to the operation's spokesman Rudi Novrianto.

"Based on our monitoring of Monday's operations, we may later decide to add to the number of ball chains, but the decision will only be made once the initial target of 374 chains have been dropped into the mud hole," he said.

Each chain comprises four concrete spheres weighing 400-500 kilograms, five of which have been dropped into the crater.

The plan was to slow the toxic mudflow which has submerged entire villages in East Java province.

Basuki Hadimuljono, the head of the team trying to plug the steaming crater, has suggested that as many as 1,000 balls may be needed.

Exploratory drilling in May last year by local gas company PT Lapindo Brantas, pierced an underground chamber of hydrogen sulphide, forcing hot mud to the surface in East Java's Sidoarjo.

The sea of mud has inundated hundreds of hectares of land and made 15,000 people homeless. It is also threatening to swamp a key railway, which is to be rerouted away from the danger zone.