Rose Byrne is to star in 'They Are Us'.

The Australian actress will portray New Zealand Prime Minister Jacinda Ardern in the forthcoming film, which will tell the story of the week following two mass shootings at mosques in Christchurch, New Zealand, in 2019, which left 51 people dead.

Andrew Niccol is to write and direct the motion picture, which will be produced by Ayman Jamal, Stewart Till, Niccol and Philippa Campbell.

For the script, several members of the mosques affected by the attack were consulted.

Niccol told Deadline: "'They Are Us' is not so much about the attack but the response to the attack [and] how an unprecedented act of hate was overcome by an outpouring of love and support.

"The film addresses our common humanity, which is why I think it will speak to people around the world. It is an example of how we should respond when there’s an attack on our fellow human beings."

Ardern was widely praised for how she handled the response to the attack, and the title for the film is taken from her speech following the shootings.

But a spokesman for the Prime Minister's office has told the New Zealand Herald that Ardern and her government haven't been involved in the movie.

And The Muslim Association of Canterbury has questioned whether the film is "appropriate right now".

Spokesperson Abdigani Ali said: "Although recognition of our Prime Minister for her response to attacks is well deserved, we question the timing and whether a movie is appropriate right now?"