Kristen Stewart admits filming 'Underwater' was ''f***ing hard''.

The 29-year-old actress stars in the William Eubank-directed sci-fi horror film - which tells the story of a crew of underwater researchers who have to scramble to safety after an earthquake - and Kristen has confessed that shooting the movie was a challenging experience.

She explained: ''It was not an easy movie to make - really long and just drippy and cold and f***ing hard.

''I want to see how we all reacted in such precarious circumstances. It really pulls out the best and worst parts of people.''

The new movie doesn't rely much on visual effects, and so the film's cast - which also features Vincent Cassel - didn't have to fake being scared.

Kristen told 'Entertainment Tonight Canada': ''A lot of stuff that we did was super practical. It was fun, it was not hard to do the movie in terms of trying to fantasise and play pretend.

''It was hard to do the movie because it was scary and it was genuine! It made a lot of these things happen, we blew a lot of stuff up.''

Meanwhile, Kristen recently bemoaned Charlie's Angels' promotional campaign, describing it as ''overly politicised''.

The Hollywood actress starred alongside Naomi Scott and Ella Balinska in the film - which disappointed at the box office - and Kristen admitted she found it ''difficult'' placing an emphasis on feminism during interviews.

She said: ''I think if I had made a movie that wasn't good and one that I wasn't proud of and a lot of people saw it, I would be devastated.

''Luckily I'm not feeling gutted because I really am proud of the movie. And I think that the kind of climate that we're living in right now is polarising and it's weird and it's kind of hard to promote a movie like that.

''And I think trying to have a really complicated, overly politicised feminist conversation in a five-minute TV interview about 'Charlie's Angels' ... I'm like 'Dude, we just wanted to have a good time.'''