Do we need a transit visa to go out of the Beijing airport?

Hi, I am travelling to bejing from London then onto Melbourne, all in terminal 3. We have a hotel booked away from the airport as our connecting flight is a 15 hour wait . do we need any sort of visa to go out of the airport , do we need to claim luggage as both flights are with air China , and if so or not what is the procedure. many thanks , please help.