"Flying home from Malaysia this morning I encountered the most confronting situation one could possibly go through," Nadia Parenzee wrote.
"I had a newborn baby take her last dying breath in my arms."
Parenzee said the baby, named Farah, had been "really restless and cried continuously" since the start of the flight.
She said she offered the parents, a Saudi couple "on their way to start a new life for themselves here in Australia", assistance as she could see they were stressed.
"As I closed my eyes to catch some sleep the Air Asia hostess tapped me on the shoulder to help her," she wrote.
"The parents offered the baby to me with desperation in their eyes I took her in my arms and immediately read Surah Fatiha (the first chapter of the Koran). Then baby Farah took her last breath and went limp. I immediately knew something was horribly wrong and shouted out to the passengers to see if there were any doctors on board."
Parenzee said what followed was two-and-a-half hours of "chaos", with resuscitation attempts continuing until the plane landed.
"Everybody was just on edge, waiting to hear that baby's breath, and that scream. And it just didn't come," Parenzee later told Nine News.
"My heart is numb and I don't know how to feel but I am honestly honoured to have held her and read a prayer on her before she passed."
"To the unbelievable staff of AirAsia you were amazing and I commend your professionalism. Rest In Peace baby Farah."
The plane was due to depart Perth again for flight D7237 at 6.50am but was delayed.
"Looks like the doctor/paramedic and police officers have come out from the aircraft," wrote one traveller on Twitter while waiting for the next flight.
The airline apologised for any inconvenience caused by the delay and said it would assist guests in re-booking.
An AirAsia statement said: "The safety and wellbeing of our guests is always our number one priority, and in accordance with procedure, the flight crew requested medical assistance on landing at Perth International Airport," an AirAsia spokesman said.
"Upon arrival, the aircraft was met by a team of medical specialists and the relevant authorities, including the WA Police. We are unable to comment further on the infants' medical situation, however our thoughts are with the infant and family involved."
Police will prepare a report for the coroner.
