Charmaine Backhouse's voice breaks when she talks about her son Isaiah.

Key points: Charmaine Backhouse claims her son's father refuses to let him travel to Australia

Charmaine Backhouse claims her son's father refuses to let him travel to Australia The father, Duncan Dobunaba, is a well-connected doctor in PNG

The father, Duncan Dobunaba, is a well-connected doctor in PNG Isaiah was born in Brisbane but has lived in Port Moresby since 2015

"The innocence of my son has been taken away and that's what breaks my heart," she said.

"I had to leave him."

Ms Backhouse last saw Isaiah in August this year when she travelled to Port Moresby to celebrate his ninth birthday.

Isaiah has been living in Port Moresby since 2015 with his father, prominent doctor Duncan Dobunaba, who is the chief anaesthetist at Papua New Guinea's health department.

When Isaiah's parents' seven-year relationship ended that year, they mutually agreed he would temporarily live with his father while she moved from Brisbane to Broome in Western Australia, Ms Backhouse told the ABC.

She said it was never intended to be a permanent situation, but there is no formal arrangement in place with respect to custody of Isaiah.

"Ever since then I have been over twice. I have kept in contact," she said.

"I've always begged [Dr Dobunaba] to bring him back and his last famous words were 'Yes I will, I'll bring him over' and nothing ever eventuated."

Isaiah was born in Brisbane, is an Australian citizen and has an Australian passport.

When he went to stay with his father in 2015 he entered PNG on a dependant visa that expired in April 2016.

Dr Dobunaba said via text message that Ms Backhouse has not been truthful and that there are "always two sides to a story".

He said "it is not entirely true" that he has refused to allow Isaiah to travel to Australia, but declined to comment further.

Isaiah was born in Brisbane and is an Australian citizen. ( Supplied )

Ms Backhouse said she had approached the Australian Attorney-General's Department for help to bring Isaiah back but was told there was little the Government could do because PNG is not a signatory to the Hague Convention on the Civil Aspects of International Abduction.

That convention provides a process for a child to be returned to their country of 'habitual residence' for custody issues to be dealt with.

International family law expert Dr Danielle Bozin said it can be extremely difficult for a parent to get a child back from a country that has not signed up to the convention.

"Essentially they'll have to engage with that country's legal process. This can be logistically and also financially difficult," Dr Bozin said.

"For example, finding a suitable qualified lawyer and also navigating a foreign legal system that can be informed by quite a different culture and potentially different ideas about what's in a child's best interest."

The Attorney-General's Department said it can't comment on specific cases and recommends parents seek legal advice in the concerned country about what options are available.

In a statement it said financial assistance may be available to cover legal costs.

After several failed attempts, Ms Backhouse has now engaged a local lawyer to obtain a court order for Isaiah's return.

"I'm extremely nervous because it's their country, it's their country's politics that scares me and because he's such a high-ranking doctor over there and well-known. He's very well connected," Ms Backhouse said.

She has also started an online petition to pressure Dr Dobunaba into sending Isaiah to Australia voluntarily.