There are three choices for you.     

1. Take flights to Guangzhou at Hong Kong International Airport. It may take you 45 minutes. Alternatively, you may take Skylimo or Airport Mainland Coach at T2 Coach Station.
   
   
2. Take Guangzhou-Kowloon Through Train to Guangzhou East Railway Station. It may take you one and an half hour.
   
   
3. Take Guangzhou-Hong Kong Express Coach at Hong Kong International Airport or other stations in the city. It may take you three and an half hours.