Several sources have been referring to loss of cabin lighting, initially when it all started. Then, we can all see they landed flaps-up, with nose gear extended. One source quoted the captain saying "that the manoeuvre was possible only due to clear sky" , indicating loss of nav equipment.
Taking a Mythbuster approach to the various bits of information:
Belly landing: Busted
Flaps-up landing: Confirmed
Loss of nav equipment: Probable
Engine fire (insinuated by one pax): Unconfirmed
Rwy overrun: Probable, (they did not neccessarily land on a rwy)
Electrical failure: Probable
Hydraulic system failure and electrical failure and engine failure/fire seems improbable, to say the least.
Over to you.