Bali police are investigating whether an Australian man and three other foreigners who tunnelled out of Kerobokan prison were helped by guards, other prisoners or someone on the outside.
They have issued a nation-wide alert, calling on locals who may have seen people with "dirty clothes" as they attempt to hunt the group down.
Shaun Davidson, 33, from Perth has found himself the subject of a manhunt after he and three others allegedly escaped the notorious Bali prison on Monday morning.
A search for the men began after 7.30am local time when a guard noticed the inmates were missing.
Tracing all along the walls, one guard spotted a cover. Below it was a hole, around 50cm by 75cm wide and 15 metres long, Kerobokan prison governor Tony Nainggolan said.
It travels underneath the prison wall and emerges at a road running along Kerobokan.
A guard tower hovers above it, but was unmanned at the time due to staff shortages.
Just two buckets, a towel, cups and sandals lay nearby.
"We will investigate if there's involvement from other prisoners or guards," Mr Nainggolan said.
Davidson was sentenced to one year in Kerobokan last September for immigration offences after he used another man's passport.
His photograph, along with his three fellow escapees have been circulated around Bali as police attempt to find the men.
Bali Provincial Police Deputy Director for Special Crime, Rudi Setyawan said it was likely that the streets where they emerged were quiet but he hopes someone may have spotted something.
"We will investigate if someone helping them from the outside. Their clothes should be dirty, right? If seeing people with dirty clothes, people should be yelling about it."
All the men are serving time for various offences at Kerobokan's Bedugul block.
Dimitar Nikolov Iliev, 43, from Bulgaria was serving a seven-year term for money laundering, alleged fellow escapee Sayed Mohammed Said - a 31-year-old from India - was in the midst of a 14-year sentence for drugs.
Malaysian man, Tee Kok King, 50, is understood to be serving seven-and-a-half years for drug offences.
Davidson has just two months and 15 days left of his sentence to serve, at which point he would have faced deportation.
He also has a warrant out for his arrest on drug offences in Perth.
When Davidson arrived in Bali in January 2015 he said he spent several months just "partying and boxing" before arousing the suspicion of authorities when he signed into a Kuta guest house under a passport with the name Michael John Bayman - claiming the photo was taken when he was "chubby".
After his sentencing at Denpasar Court last year, Davidson told AAP how he spent his first few weeks in custody crammed into a small cell with 20 other people.
Despite overcrowding in Kerobokan, he said it wasn't the "living hell" he thought it would be.
Prison escapes in Indonesia are not unusual.
Just last week, 76 inmates escaped Jambi jail in Sumatra after flooding caused the prison's walls to collapse.
In May, in another Sumatran facility, Pekanbaru, 442 prisoners made a run for it following allegations of guards charging people for cells in the chronically overcrowded facility.
© AAP 2017