Chinese snowboarder Jiayu Liu took a serious spill in a disastrous move on her women's halfpipe qualifying run Wednesday ... slamming down hard and unable to get up afterward.

Check out the scary video ... the 33-year-old was well on her way to landing a 900-degree spin ... but her board suddenly caught an edge as she was coming off the transition part of the pipe, violently tossing her forward and sending her into an uncontrolled somersault.

The clip shows her legs and board flipping over her back -- a wipeout known as a "Scorpion," because the crash resembles the arachnid's tail curling up forward toward its head.

Liu slid to a halt and laid there, only slightly moving her head ... clearly in pain. Medical personnel hopped into the halfpipe to help her, and she was carted away.

Neither the Olympics nor Liu's team shared an immediate update on her status.

She was in 13th place when she descended into the pipe and needed to move up one spot to qualify for finals, which will be held Thursday.