'Pitch Perfect' Star Oops My Candle Torched My Condo Bldg.

9/27/2014 12:30 AM PDT

'Pitch Perfect' Star Alexis Knapp -- Oops ... My Candle Torched My Condo Bldg.

Alexis Knapp's kumbaya moment with a candle went up in flames ... and so did her condo bldg.

Alexis -- famous for her roles in "Project X," "Pitch Perfect" and "I'm Ryan Phillippe's baby Mama" ... left her unit with a candle still burning and it caught something on fire which ignited the blaze that engulfed the entire building ... according to the L.A. Fire Dept.
It took 75 firefighters, 30 fire trucks and 3 separate agencies to knock down the blaze.  The damage is so extensive the building is now red tagged. 

A firefighter was injured ... which could be a problem for Alexis.  

But there's good news ... a couple of cats were rescued.

We reached out to Knapp for comment ... so far, no word back.