Teresa Palmer and Mark Webber have announced the birth of their fourth child together.

Daughter Prairie Moon is the latest addition to the family of Australian actress Palmer and her American actor and screenwriter husband Webber.

On Thursday, both made posts on Instagram announcing the arrival of Prairie Moon, sharing photos of the new girl, alongside their other children; sons Bodhi, seven, and Forest, four, and two-year-old daughter Poet.

"Introducing our daughter, Prairie Moon Palmer, who was born just as the sun rose on Tuesday morning, 17th August, surrounded by her siblings who are absolutely enamoured with her," the Hacksaw Ridge actress told her 1.2 million followers, adding, "A little magic moon for our family".

Snow Day actor Webber shared a photo of him holding his newborn daughter, with the caption: "My heart has grown 5 times bigger. Welcome to the world my little magic Prairie Moon."

Underneath the image, Palmer commented: "My little dreamboat".

Scott Pilgrim vs. the World actor Webber is also the father of 13-year-old Isaac from a previous relationship with Mr. Robot actress Frankie Shaw.

Palmer and Webber have been married since 2013, and worked together on 2014 drama film The Ever After.