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ll mining activists in Sawahlunto, West Sumatra, are at a standstill after a major underground explosion killed at least 31 miners and buried 12 others, officials said Wednesday.

They added the 12 missing miners were feared dead after being trapped underground for more than a day.

The order to halt all mining activities was issued by Sawahlunto Mayor Amran Nur to 13 coal mining firms operating in the area, including PT Detras in Bukit Bual, where the fatal blast occurred Tuesday.

"Company operations have been temporarily closed until they comply with proper mining procedures and ensure the safety of miners," Amran said at his office in Sawahlunto.

The explosion may have been caused by a buildup of methane gas in the mine.

Amran said the Sawahlunto mining office had tried to prevent accidents in the mine by reviewing operations after examining the levels of methane gas in the mine.

"But miners expelled and chased away officials assigned to investigate the site in December 2001," he added.

The mayor admitted the levels of methane gas in the mine were dangerously high due to a lack of ventilation.

"We issued a letter asking them to add additional ventilation, but we didn't know whether they had abided by it or not. We didn't check it again," he said.

Rescue workers estimate the death toll to 31.

Rustam Pakaya, the head of the Health Ministry's disaster center, said in a text message that at least 12 more miners were still missing, Reuters reported.

As many as 16 bodies were retrieved on Tuesday, and another 14 on Wednesday, rescuers said. Most of the bodies sustained severe wounds and could not be identified.

Alexander Tarigan, who leads the rescue team from PT Allied Indo Coal (AIC), said the explosion did not disturb the structure of the mine and had not compromised the rescue efforts.

Rumainar, a member from the West Sumatra disaster management task force, said data from his emergency post at the blast site recorded that 32 miners were trapped in the mine.

He could not say exactly what had triggered the explosion.

"There are two versions. One says it was caused by a short circuit in the power generator, while another claims it was caused by a miner smoking.

"Which story is correct cannot be traced because all witnesses have all been killed," Rumaniar said.

Sawahlunto Police chief Adj. Sr. Comr. Ano Sunarno said all mining operations had been suspended to allow for an investigation.

After the investigation is completed, he added, the police would coordinate with the local administration to determine whether to allow mining activities in the area to continue.