Saoirse Ronan and Timothée Chalamet are a ''bonfire of chemistry''.

The 'Lady Bird' co-stars have teamed up again to play Jo March and Theodore 'Laurie' Laurence in Greta Gerwig's big screen adaptation of Louisa May Alcott's 'Little Women' and the director believes they are one of the ''great cinematic pairings''.

Speaking to PEOPLE and Entertainment Weekly about Saoirse, 25, and Timothée, 23, Greta said: ''There is some true pairing between them that feels like what's in the tradition of great cinematic pairings. They have an energy between them that is like they become a bonfire when they're together. They're both so alive and they're both so talented and so smart and so young. When you put them together it's like combustion.

''[Watching them] breaks my heart, every time. They are both wonderful dancers. I think of them as my children, I just adore them. They are spectacular actors. I don't know how they do it, I mean it's magic. I direct them, but it's all there.''

Greta also praised Emma Watson, who stars as Jo's sister Meg March in the new movie.

She said: ''To me she embodies everything that I was interested in, in terms of who the March women were. She is lovely, she is way out there trying to do everything she can [with her activism]. And I think, in terms of what she did with the character of Meg, she has so much open-heartedness and so much love combined with that much intelligence, it's heartbreaking and potent. Because she's absolutely herself with understanding the struggle of who that character is.''

The movie also stars Eliza Scanlen and Florence Pugh as Beth and Amy March, with Laura Dern as the March matriarch Marmee and Meryl Streep as Aunt March.