Australian Shaun Davidson in four-man Kerobokan prison breakout

Four foreigners - including Australian Shaun Edward Davidson - escaped from the prison via a tunnel.

Bali corrections chief Surung Pasaribu confirmed Davidson, who had just 2½ months of his one-year jail term left to serve, was among the escapees.

A source at Kerobokan jail told Fairfax Media the foreigners had last been seen at sahur - the term for the predawn meal before fasting begins during Ramadan. 

"They are still investigating whether they escaped through the waste ground tunnel behind the clinic. It is filled with water," the source said.

The escapees included a Bulgarian, an Indian and a Malaysian.

Davidson was jailed for a year last August after he was found guilty of misusing a travel document belonging to someone else.

He had been due to face Perth Magistrates Court on January 28, 2015, charged with possessing methamphetamine and cannabis and two other offences.

When he did not attend, an arrest warrant was issued.

But instead of going to court, Davidson skipped the country, arriving in Indonesia on a one-month tourist visa

Davidson said he lost his passport. He said he had contacted the Australian passport office and reported his own missing, but then began using a passport under the name of Michael John Bayman, which Davidson said he had found in a hotel room.

Bali immigration authorities told Fairfax Media the passport had been reported missing by its real owner in 2013.

In an interview with Fairfax Media between the bars of a holding cell at Denpasar District Court last September, Davidson said the conditions in Kerobokan were bearable if one had money and support from the outside.

He said he had been expecting a "living hell" when he was incarcerated in April last year after being named a suspect. 

Davidson had spent the year before he was apprehended boxing and partying.

But he came to the attention of authorities in March last year when he was staying at Rabasta Hotel in Kuta.

Ngurah Rai airport immigration officer Mohamad Soleh told Fairfax Media in April last year that a report was made of a foreigner staying in Kuta who was suspected of overstaying his visa.

When immigration authorities investigated, they found he had not only overstayed but was using a fake identity.

Of the other escapees Bulgarian Dimitar Nikolov Iliev was jailed for seven years for money laundering, Sayed Mohammad Said was jailed for 14 years on drug charges and Malaysian Tee Kok King bin Tee Kam Sai was jailed for seven years on drug charges.

Sayed Mohammad Said was the last prisoner seen during morning prayers and again at 6.30am this morning.

The waste tunnel, through which the four prisoners are believed to have escaped, was 15 metres long and half a metre wide.