The newcomers are, in a word, gross. They showed up, a million of them, on South Africa's doorstep 20 years ago. And they won't go home.

They steal. They're violent. They breed like insects. They have vile dietary needs.

And after holding them for two decades in a vast walled-in shantytown, the government and "the people" have had enough. The grotesque creatures — 1.8 million of them, charitably nicknamed prawns — are to be forcibly evicted by "contractors" and sent to a concentration camp.

Nobody seems to mind. When you're a prawn, the "Humans Only" signs, the restrictions on movement, breeding and land ownership are the best you can expect in District 9, a splatter-happy sci-fi film that slides in a sociology lesson among the exploding heads.

Johannesburg native Neill Blomkamp's film (he wrote and directed it) is equal parts Independence Day and Alien Nation, with a dollop of Blair Witch shaky-cam and Robocop gunplay tossed in for good measure. But what it really aspires to is to be a sci-fi Black Like Me. Only when Wikus van de Merwe (Sharlto Copley), the officious, sweater-vested bureaucrat in charge of the "evictions," becomes hunted like the aliens can he feel their pain.

Blomkamp tells this story as a documentary flashback, experts "remembering" events mixed in with TV news segments, footage from a Wikus-at-work documentary and surveillance video. The point of view isn't consistent, but the camcorder stuff gives District 9 immediacy. We see Wikus lead his team into the shantytown and see what causes him to slowly develop sympathy for aliens who look like shrimp clad in ill-fitting human rags.

Corporate skulduggery, medical experiments and trigger-happy mercenaries (led by David James, scary) conspire to open Wikus' eyes to the inhumanity of this situation — even if the creatures they're dealing with aren't human.

The movie settles too comfortably into a bloodbath last act, but Blomkamp nicely pulls the trigger on the big action beats even as he ratchets up the tension. Amazingly, he manages to make these squishy beasts sympathetic — eventually.

As allegory, District 9 isn't all that, despite the racist parallels and the natural advantage of being set in South Africa. But as straight sci-fi action, it packs a punch, once you get past the ick factor.