A teen mum is in a desperate fight to stop her 18-month-old daughter leaving Australia.

A Melbourne teen mother is in a desperate legal bid to stop the foster parents of her young daughter from moving overseas.

According to the Herald Sun, the young woman – who cannot be named for legal reasons – is concerned she will never see her 18-month-old daughter again if the couple caring for her leave the country.

The couple, who are aged in their late 50s, have applied to the Children's Court for permanent custody of the toddler, and are believed to be making plans to leave Australia.

The pair are not permanent residents, and one was offered a job overseas. The other stepped down from their job in preparation for the international move.

The couple have had custody of the baby for less than a year, and there are no allegations of wrongdoing on their part.

They have submitted the application in order to get passport proceedings for the 18-month-old started.

The young mum told the Herald Sun she has not been given a chance to be a mother to her own daughter.

"Once she is out of the country, she is gone. She is not coming back," she said.

"I want to be a mother to her. I have not been given that chance."

The Department of Health and Human Services has processed a plan for the foster parents to return to the country four times a year so mother and child could see each other. However, once the foster couple is out of Australia, there is no power to enforce the agreement.

According to the Herald Sun, family law experts say the case could "set a dangerous precedent" for overseas couples to sidestep Australia's strict adoption rules.

The foster family is yet to comment on the matter.