Mud, gas and boiling water that have been gushing out of the ground in East Java since May, submerging half a dozen villages and 20 factories, could continue for a century with "catastrophic consequences", European experts said yesterday. Efforts to seal the channels through which the mud is escaping are unlikely to succeed, and it is impossible to tell how much fluid remains underground, according to a University of Oslo geology team.

"It's unlikely to stop permanently for a long time," Adriano Mazzini told a press conference in Jakarta. "It's hard to say when the overpressure will have been fully released. It could be one, 10 or 100 years. But to seal it will be very, very difficult." According to Mr Mazzini, unless the flow stops soon, the affected land, which has already starting sinking, could subside significantly. "It will be catastrophic," he said.

The mud started flowing on May 29, a couple of hundred metres from where the gas company PT Lapindo Brantas was drilling an exploratory well nearly two miles deep. It has been gushing up to 50,000 cubic metres a day - or two large bathsfull a second - ever since.

At least four villages will almost certainly have to be destroyed, and two others have been flooded. More than 11,000 people have evacuated their homes.

On September 8, the central government, fearing a political disaster as well as the environmental impact, took command of the operation to stem the flow, control the flood (which now covers about 400 hectares (1,000 acres) and supervise the social programmes for the affected communities. A spokesman for the government team told the Guardian the latest findings were "useful and worrying". He said: "They show we still have a lot of work to do."

Observers said the president, Susilo Bambang Yudhoyono, had been wise to intervene. "This could be the achilles heel of this government," said Dennis Heffernan, a political and business consultant. "Unless more resources are put to work, we're in danger of a catastrophe on the level of the Exxon Valdez."

The Exxon Valdez was an oil tanker that sank in Alaska in 1989, causing widespread environmental devastation.

All the expenses are being borne by Lapindo, which is controlled by the family of Indonesia's senior welfare minister, Aburizal Bakrie. Estimated costs are thought to be well over £70m, while the company's insurance only covered £15m.

Mr Mazzini, whose team has studied mud volcanoes for more than a decade and spent just under a week on site, said it was impossible to say conclusively whether the drilling caused the disaster.

There has been speculation that the disaster was caused by Lapindo failing to use a proper casing during drilling. Mr Mazzini said this was unlikely. "This is a huge case of overpressure," he said. "A casing would not have made any difference, I don't think. But I'm not a drilling expert."

The mudflow is thought to have been caused by one of four possibilities: gas-charged fluids breaching coral mounds on top of the limestone rock; a magmatic reaction generating gas; a new-born mud volcano; or hydrothermal fluids migrating from neighbouring areas.