Ask him to stop for food ("sufan" in chinese) and get the police involved. The police will either get you to get another taxi driver and send this one home for not putting on the meter or this driver will agree to put on the meter and you'll have to negotiate for the distance you travelled. It is completely illegal for him not to put on the meter even if you negotiated a rate.

Honestly you have put your well being into serious danger as these drivers can get really crazy in such cases.