The source said the tunnel was 15 meters (50 feet) long and ran under a number of rooms before passing under a road at the Yongah Hill Immigration Detention Centre, around 100 kilometers (62 miles) east of the city of Perth, Western Australia.
The tunnel had passed the first of three perimeter fences, the source said, and it was anticipated that two more months of digging would be needed to reach the outer fence.
The Australian Border Force (ABF) told CNN a “suspected attempted escape” had been prevented at the center following the discovery of the “partially dug hole.”
All detainees had been accounted for, and the matter had been referred to the Australian Federal Police (AFP), an ABF spokesperson said in a statement.
The tunnel’s presence was first revealed by Ian Rintoul, from the Refugee Action Coalition (RAC), who said on Tuesday that immigration authorities had found a 20-meter (65-foot) tunnel beneath a detainee’s room.
The source told CNN a number of detainees used whatever utensils they could find to dig the tunnel, including parts of a fridge and a wooden drawer. They worked whenever guards weren’t looking, using the lights on their mobile phones and candles to continue digging, he said.
Pillow cases were used to carry dirt from the tunnel before it was scattered in a 50-centimeter (20-inch) gap between the floor of the room and the ground, where it couldn’t be easily seen from the road, the source said.
An image provided by the Refugee Action Coalition shows tape blocking off a number of low-set rooms, including 6F, the room above the tunnel.
According to the latest government statistics, 315 men were being held at the Yongah Hill center as of February 28. Most were so-called “501s” — people who have had their visas canceled under section 501 of Australia’s Migration Act, which allows the government to revoke visas on character grounds, including if visa holders have committed a serious crime.
Any crime committed during an attempted escape from a detention center is grounds to fail the character test, according to the act.
As of late February, about 1,500 people were being held in immigration detention in Australia, mostly from Iran and New Zealand. Most were held for more than one year, and 106 had been held for at least five years.
Rintoul, from RAC, says the attempted escape “highlighted the prolonged detention of those being held in the onshore detention regime.”
Human rights advocates have long criticized Australia’s immigration policy, including its offshore detention program, which saw hundreds of refugees and asylum seekers held in detention centers on Manus Island in Papua New Guinea and the Pacific island nation of Nauru.
In July 2013, the government announced that no asylum seeker who arrived by boat would ever be allowed to settle in Australia.