Surfer Jamie Mitchell — widely regarded as one of the best all-around athletes in the sport — had a freak accident riding waves in Hawaii this week … suffering brutal gashes to his face, throat and head.

Mitchell, 48, described what happened in an Instagram video … stating he was hit by the fins of his big-wave board while surfing one of his favorite waves on Tuesday.

The Australian surfer shared evidence of his bloody injuries before he got bandaged up … and they’re pretty gnarly. You can take a look at the rest of ’em on your own terms.

“Something like 18 staples in the back of my head. Got 15 stitches down in my throat, five in my cheekbone, and another couple somewhere here, but I’m going to be okay.”

Mitchell — a 10-time Molokai 2 Oahu Paddleboard World Champion — thanked bystanders who helped him get to shore … as well as the Kahuku Emergency crew for the medical care.

Mitchell posted an update video on Thursday … telling his fans he’s healing up and there are no signs of infection.