She was celebrating her 21st birthday when her partner Chandler Powell proposed at the Irwin-owned Australia Zoo "surrounded by animals" where they met.

The daughter of Steve Irwin, best known as The Crocodile Hunter, announced her engagement on social media on Wednesday, posing with a diamond ring.

"On my birthday I said 'yes' and 'forever' to the love of my life," Irwin wrote on Instagram.

"Chandler, close to six years ago I fell in love with you and every day since has been a whirlwind of adventure and true happiness. I'm so looking forwarding to spending our forever together as your wife. Here's to a lifetime of friendship, purpose and unconditional love.

"Now let's get married already!"

Powell, a wakeboarder from the United States, said he proposed at the family zoo on the Sunshine Coast where they first met and where he now works.

"She said YES! Almost six years ago we met at Australia Zoo. I immediately fell head over heels for her kind and thoughtful heart that radiates so much light," he wrote on Instagram.

"Proposing in her very favourite place in the zoo, surrounded by animals, seemed like the perfect way to embark on this incredible new chapter in our lives. Bee, I love you more than anything in this world and I always will. Happy Birthday."

Mum Terri Irwin said her father would have been "so very happy" if he was still around on the "best day ever".

"Chandler asked and beautiful @BindiIrwin said yes. I am so very happy, and I know Steve would be too."

Her brother Robert Irwin, said he was "beyond happy" for the couple.

"You are true soulmates and have always been so completely perfect for each other," he wrote.

Powell responded that it was a "blessing to have gained a future wife and also a brother".

Thousands of fans left enthusiastic messages of support for the couple on their Instagram posts.

Celebrities rushed to congratulate the couple too.

Stranger Things star Millie Bob Brown commented on Irwin's Instagram post, while Lisa Origliasso, of pop duo The Veronicas, congratulatd the "beautiful souls" and "undeniable soul mates". Australia Zoo's Instagram account commented: "We're so excited for you both! This is the best news ever!!"

Dad Steve Irwin died in September 2006, aged 44, when a stingray barb pierced him in the heart while filming for documentary Ocean's Deadliest near Port Douglas in Queensland.

His daughter went onto have her own international career in television and conservation.