The parents of an 18-month-old baby girl - diagnosed with a-one-in-a-million cancer - have taken her journey to Facebook.

Since Mia Fletcher's liver cancer diagnosis in September, strangers have been able to track the brave little girl's progress on a special Facebook page, created by her parents Jason and Jodi.

Doctors say there's a tumour the size of a grapefruit on little Mia's liver.

"It's bad enough if an adult gets cancer, but a baby, that's really hard," Mia's dad Jason told Seven News reporter Karen O'Sullivan

"She hasn't even had a chance to get outside and play yet and she's got this cursed thing. It's just terrible."

While chemotherapy has shrunk the 14-centimentre tumour, it's too dangerous to remove, and now more tumours on her lungs are being treated.

The response to Mia's cancer journey has been overwhelming for her family, and they intend on keeping her followers updated in the coming weeks and months.

"You've got more people coming forward that you don't know, than people you do know," Jason said.

"You wouldn't think people care, but they do," Mia's mum Jodi added.

Mia's cancer journey documented on Facebook. Photo: Facebook

With only one in a million children diagnosed with this type of cancer, Mia has a long journey to recovery.

"She's hanging in there, we're all trying our best to get her through this," Royal Children's Hospital Oncologist Dr Martin Campbell said.

"She's a little trooper," Jason added.

Mia is expected to spend Christmas at the Royal Children's Hospital.

"I am praying so hard that this works, thank you for all your support and well wishes, kisses from Mia," her Facebook status reads.

Use the bank details below to donate to Mia's cancer fund: