Australian Associated Press yesterday quoted operations spokesman Rudi Novrianto as saying the flow of mud coming out of the crater suddenly stopped for about 30 minutes shortly before noon (4pm AEDT) on Monday.

“None of our team members knows for sure what happened and we are still trying to determine how it happened,” AAP quoted Novrianto as saying.

The volcano, in East Java, just bubbled during the pause, he reportedly said.

The temporary pause was the first since the volcano began spewing mud near the Banjar Panji-1 exploration well last May.

Indonesian experts are trying to stem the flow by dropping chains of heavy concrete balls into the funnel.

Numerous other efforts to cap the flow have failed.

AAP reported, however, that Bagus Endar Bachtiar Nurhandoko, an official from the team battling the crater, told the Kompas newspaper that the pause was probably unrelated to the hundreds of chains already dropped into the mud hole.

He said the brief pause might have happened because parts of the funnel collapsed, creating a temporary obstruction that was eventually cleared by pressurised gas in the crater.

Experts have already dropped 374 chains, each comprising four concrete balls, into the crater as part of a plan to narrow the funnel and obstruct the mud to reduce the flow by about 70%.

The team working on stopping the flow intend to sink another 500 chains into the mud hole, but the team is reportedly still awaiting a new supply of concrete balls.

By latest accounts the mud is now threatening to swamp a key railway, which is to be re-routed away from the danger zone.

Australian company Santos holds a non-operating 18% stake in the Banjar Panji exploration well venture, in partnership with Indonesian operator Lapindo Brantas and PT Medco Energi.