There is info on /r/TeslaMotors [1] indicating it started near the front of the vehicle. Either an electrical component forward of the passenger compartment, or something in the front luggage compartment (where the motor typically would be in an ICE vehicle).
I forget exactly what it is but there is an important component of the charging system in the front right wheel well that you are not supposed to cut through if you are attempting a rescue of the passenger in a Tesla. They demonstrated that in their emergency responder training videos, saying that it's different from normal cars where you can cut right through the wheel well and here you should not since there are high voltage wires there.