Miley Cyrus engaged to actor Liam Hemsworth

Actress Miley Cyrus poses at the premiere of ''The Hunger Games'' at Nokia theatre in Los Angeles, California March 12, 2012.

NEW YORK (Reuters) - Miley Cyrus, the former Disney Channel child star whose growing pains have been played out in the glare of the world's media, announced her engagement on Wednesday at the age of 19 to "Hunger Games" actor Liam Hemsworth.

Cyrus, whose "Hannah Montana" TV series made her a teen idol, said she was engaged to marry her Australian boyfriend Hemsworth, 22, after a three-year romance.

The news quickly became one of the world's top trends on Twitter, bringing thousands of congratulations from fans, as well as questions over the wisdom of settling down so young.

Cyrus and Hemsworth have been dating on and off since meeting in 2009 on the set of film romance "The Last Song".

"I'm so happy to be engaged and look forward to a life of happiness with Liam," Cyrus told People magazine.

"Thank you for all the love today. I'm happy to share this news with you all. I feel like all my dreams are coming true," the young star posted on Twitter.

Cyrus's father, country singer Billy Ray Cyrus, who starred with her on "Hannah Montana", said he was delighted.

"All I ever hoped for as a daddy was to see my kids reach their dreams. To find happiness, peace of mind, and someday know true love," he told celebrity website HollywoodLife.com.

Hemsworth proposed on May 31 with a 3.5-carat diamond ring, according to People magazine. No wedding date was announced, but talk quickly turned to whether they were too young for such a commitment.

"A 3.5-carat diamond ring and an Australian fiancé sound like a fairytale marriage, but teen pop star Miley Cyrus's engagement raises questions about the idealized dream she's modeling for the average teenager. In other words: Can teen marriages last?" asked Allison Terry, writing for the Christian Science Monitor.

The engagement was the main topic on female TV chat show "The Talk" on Wednesday, where "America's Got Talent" judge Sharon Osbourne spoke up for the singer.

"I think that she is 19, but in her head she is an old soul. She has lived 19 lives in 19 years ... She is an accomplished young woman, who knows what she wants at this time in her life," Osbourne said.

Fans of the starlet once known as "Smiley Miley" could barely believe how the time had flown. "Miley Cyrus and Liam Hemsworth are ENGAGED? OMG I remember watching her on Hannah Montana for the first time. my bby grow up so fast :')" tweeted one fan, Hatoon.

Cyrus was 12-years-old when she landed the part of a pop star by night and regular schoolgirl by day in Disney Channel's "Hannah Montana".

The role launched Cyrus as an international, chart-topping singer with hits like "Best of Both Worlds," "The Climb" "7 Things" and "Party in The USA".

But when Cyrus quit the show at age 16, she also moved fast to shed her squeaky-clean image, performing in sexy outfits, making raunchy music videos and shocking fans by smoking the hallucinogenic herb salvia on her 18th birthday.

Cyrus put her music career on hold two years ago to focus on acting, but her latest film "LOL" was a box office flop that was quickly released on DVD.

And not everyone was feeling the love for the young couple.

"Miley Cyrus and Liam Hemsworth are engaged. Please excuse me while I stick my head in an oven" tweeted Girl's Got Issues.

(Reporting by Jill Serjeant and Christine Kearney; Editing by Bob Tourtellotte and Leslie Gevirtz)