Alt-right groups are being foiled in their attempts to sabotage a superhero film with an all-black cast.

Facebook has shut down a group which is bombarding Marvel's unreleased movie Black Panther with negative reviews.

Rotten Tomatoes is actively banning reviewers who use hate speech.

NZ Herald entertainment writer Karl Puschmann says the group's intentions are clear.

"The movie's not out yet, they haven't seen it but they're posting bad reviews and trying to [get] studios to not invest in these films that feature minorities, females, diverse casts."

He says it's not the first time organised review spam has taken place, with a similar campaign making the 2016 Ghostbusters trailer the most disliked in YouTube history.

Puschmann says it's a noble effort on the sites' part, but the internet is notoriously difficult to police.

"You can sign up. You're a member now, you can just post your thoughts online, and if your thoughts happen to be racist, alt right thoughts, trolling thoughts, it's going to be like Whack a Mole, trying to knock you down before you can get going."

Black Panther, due for release in New Zealand next week, is the first Marvel superhero in over a decade to have a black lead.

It stars Chadwick Boseman, Lupita Nyong'o and Angela Bassett.