I don't have anything to source but from a friend of mine working on this he indicated that it's being classified as a "runway excursion" initially by investigators. Some of the key possibilities they're looking at based on aircraft positioning and environmental observations are an aborted takeoff, a wildlife strike and a catastrophic failure of aircraft components. Obviously this is the most preliminary information and I only obtained it by casual conversation.
He also pointed out that the initial assessment is subject to change based on new evidence.