An American zoo is marking the third birthday of a hippo who was born prematurely by raising money for Australian wildlife affected by the recent wildfires.

Instead of sending birthday gifts for Fiona, Cincinnati Zoo in Ohio is asking people to buy T-shirts that will directly benefit the Bushfire Emergency Wildlife Fund.

The T-shirt features a koala and kangaroo giving Fiona a hug and says: Supporting Our Friends Down Under.

Hippo Fiona eats her birthday cake
Fiona eats her specialty birthday cake (John Minchillo/AP)

All proceeds from sales of the tops will be sent to Zoos Victoria to help them care for suffering animals.

The zoo will add 5,000 dollars (£3,800) to the total amount raised.

Fiona became a global celebrity after she was born prematurely on January 24 2017, weighing in at just 29lbs (13kg).

The normal range for a hippo’s birth weight is 55lbs to 120lbs (25kg to 55kg).

Hippo Fiona swims after eating her specialty birthday cake in her enclosure at the Cincinnati Zoo & Botanical Garden
Fiona swims after eating her birthday treat (John Minchillo/AP)

Fiona now weighs a healthy 1,300lbs (590kg), according to the zoo.

“Fiona won the hearts of Cincinnatians when she fought to survive after being born six weeks early and terribly underweight,” Cincinnati Zoo director Thayne Maynard said.

“Three years later, people all over the world are still crazy about this normal, healthy hippo.”