J.K. Rowling is "still learning" how to write screenplays.

The 51-year-old author has been capturing children's imaginations since 1997 when she released the first 'Harry Potter' book and has since become a world renowned writer, but says she still struggles when it comes to writing the screenplays for the movie versions of her hit novels.

Speaking at the premiere of her 'Harry Potter' spin-off 'Fantastic Beasts and Where to Find Them' in New York City, the author said: "It was intense. I was learning to write a screenplay while writing a screenplay.

"It's a totally different thing to novels. It was a real challenge. To tell you the truth, I loved that. I am still learning."

But screenplays are something the writer will have to get used to, as the spin-off movie - which was originally supposed to be a stand-alone feature - has been slated for a five-part series with the author working as a screenwriter on all the installments.

Answering a fan question on Twitter, she wrote: "I'm the screenwriter. Currently putting the finishing touches to the second one."

The Eddie Redmayne-fronted movie franchise then posted on its own Twitter account: "@jk_rowling has just confirmed the magic continues in a total of FIVE MOVIES! We can't wait #FantasticBeasts (sic)"

Meanwhile Bonnie Wright - who played the flame-haired Ginny Weasley in the original film series - believes the series is a hit because it offers people a world they can "escape to".

She said at the premiere: "['Harry Potter' is a hit because of] the themes of loyalty and friendship and love . . . Something we all strive to live by. When the world can sometimes be challenging, people love a world to escape to."