BOLAANG MONGONDOW, Indonesia (Reuters) - Indonesian authorities on Wednesday ramped up efforts to find 37 people feared buried by the collapse of an illegal gold mine on the island of Sulawesi that killed at least four people.

Rescuers used spades and ropes to pull out 19 badly injured miners and found four others dead. Officials said they could hear the voices of some of those trapped in makeshift mining shafts in a muddy hillside in the Bolaang Mongondow area of North Sulawesi province, and believed many were still alive.

“We are able to detect that many of them are still alive because we can hear their voices, as there are some places where air is getting in and out and there are gaps in the mud,” Abdul Muin Paputungan of Indonesia’s disaster agency said by phone.

The injured were carried on stretchers and in ambulances to a nearby hospital, where families had gathered to wait for news.

Indonesia’s disaster mitigation agency said at least 60 officials and volunteers were involved in the rescue effort but were using simple tools because conditions remained dangerous, with the land still prone to shifting and sliding.

The Indonesian government has banned such small-scale gold mining projects, although regional authorities often turn a blind eye to the practice in more remote areas. With little regulation, such mines are prone to accidents.

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PATCHY RECORD

Disaster agency spokesman Sutopo Purwo Nugroho said dozens of people had been mining for gold when beams and support boards broke suddenly. “Evacuation efforts continued through the night because of the number of people estimated to be buried.”

The issue of mining safety was thrust back into global prominence this year after a dam in Brazil holding back mining waste burst, killing more than 300 people.

Resource-rich Indonesia has a patchy record on mining safety, particularly small-scale unlicensed mines. At least five people were killed in the same area of Sulawesi last year after an illegal mine collapsed during heavy rain.

Agung Pribadi, a spokesman for Indonesia’s mining ministry, said by phone three mining inspectors had been sent to assist in the rescue and that illegal mines had recently been shut in the area. “Maybe now they have started again,” he said.

The area is also home to a gold mine operated by PT J Resources Asia Pasifik, where production began in 2013.

The company said in a statement that illegal mining remained rife in the area and had caused deaths before.

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Gatot Sugiharto, who heads a group called the Citizens Mining Association, estimated there were about 200 similar unlicensed mines around Indonesia, with 10 in that area of Sulawesi alone.

He said such mines operated in a grey area, with authorities reluctant to give them permits because it would mean official supervision and attention to safety.

Sugiharto estimated that an experienced miner might be able to survive for up to three or four days under the rubble if they could find air pockets and were not crushed by rocks.

“They can breath slowly and usually they don’t panic. If there is no poisonous gas they can survive for some time,” he said.

(This story corrects the death toll to 4 throughout)