If go by bus, you should get to Shenzhen henggang or Baoan bus station to catch direct buses. Shenzhen is about 900km from Qinzhou, that is to day, you need at least 8 hours to get to Qinzhou from there. Other option, go to Guangzhou East from Hung HOm station by East Rail. Then change another train to Nanning, which is 1.5 hours from Qinzhou by bus.