from L visa to apply for working visa

Hi, Is it easier to convert or apply L visa to working visa? i have an L visa when i enter china then i found an employer she told me to apply for working visa here in philippines i already have an invitation letter of duly authorized unit and an alien temporary work permit. i also have relatives who lives there. what additional documents do i need to present in applying a working visa? do i still need to provide a new bank certificate and a get a new NBI clearance ?thanks