Universal’s live-action “How to Train Your Dragon 2” has hit a rough patch before cameras even finish rolling … ’cause a crew member just lost multiple fingers in a brutal accident during production.

A source with direct knowledge tells TMZ … a special-effects tech working at the UK’s Sky Studios Elstree severed multiple fingers on one hand earlier this month during an incident involving a saw in a workshop tied to production.

Doctors tried to save the severed digits, but they couldn’t be reattached, despite surgery.

Details around exactly how it happened are still unclear … but it’s a seriously grim start for a major studio project.

The film’s being directed by Dean DeBlois — who helmed the original animated franchise — with this live-action version slated to drop June 11, 2027 … after kicking off filming at Sky Studios Elstree back in February.