A Swedish black metal band sprayed pigs blood on concertgoers during a Satanic ritual … triggering a vomit-fest in the audience … and we got the disgusting footage.

Watain —  whose members are devout devil worshipers — played their only U.S. summer gig Sunday night in Brooklyn … and they were true to form.

You see the lead singer present the audience with a goat skull full of animal blood … then drench the crowd.  According to interviews with the band, they use real pig’s blood.

You hear audience members shriek … and we’re told some barfed and cried.

Shockingly … cops say no one complained.  And no one has heard a peep from the health dept.