Dear Pak Lee,
Thanks for contacting Top China Travel!
The KCR East Railway travels between Guangzhou East Railway Station and Hong Kong (Hung Hom station in Kowloon). Tickets can be bought in Guangzhou East station or at Hung Hom station in Hong Kong, upon your arrival in the stations by person. You can also buy tickets on line at http://www.it3.mtr.com.hk/b2c/frmIndex.asp?strLang=Eng 14 days in advance from the KCR website.
So you can try book the train tickets online before you depart from your country. Or you can take a taxi to Guangzhou East Railway Station to buy it upon your arrival in Guangzhou Baiyun Airport. (Note: Tickets for Foshan and Zhaoqing to Hung Hom can be bought from ticket sales outlets in the Mainland only.)
The train journey time is generally under 2 hours and there is food and drinks service on the train. Foreign passengers in Guangzhou and Hung Hom station are advised to arrive 45 minutes before departure. And gates close 10 minutes before departure.
Any further request or question, please feel free to contact with us.