Can I buy a ticket from Shenzhen to Shanghai while in Hong Kong?

There are plane, ferry and train that go direct from Hong Kong to Shanghai. Plane takes about 3 hours, the other 2 will take 1 or more days. Simply walk into any travel agents in Hong Kong to enquire, there're many agents that deal with the Mainland tickets located in Sheung Wan or the Western District. The agents in HK should all understand English.