Changing to L visa to Z visa

According to China visa regulation, you need to apply for a Z visa outside of mainland China. But it is possible to change an L visa into Z visa within China, say if through visa agency. But if you have already planned to go out for two weeks, you can apply for a work visa Z in HK by yourself. Time is far enough. So, better leave China (on L visa) with documents required from your employer and related departments.