Complex sentence: Simoncelli suffered much more severe injuries and was taken by ambulance to the circuit's medical centre, and at 16:56 local time, less than an hour after the accident, it was announced that he had died from his injuries.
Split into simpler sentences: Simoncelli suffered much more severe injuries and was taken by ambulance to the circuit's medical centre. At 16:56 local time, less than an hour after the accident, it was announced that he had died from his injuries.