If you enter Zhuhai(https://www.travelchinaguide.com/cityguides/guangdong/zhuhai/) and Shenzhen(https://www.travelchinaguide.com/cityguides/guangdong/shenzhen/) for sightseeing or visiting relatives, you need to apply for a seperate Tourist visas (L-visa), regardless of the availability and validity of your Crewmember visa (C-Visa). However, if you on the work of international air, maritime and train transportation, you can enter Zhuhai and Shenzhen with your C visa.