Train possibility

Hello,

The situation is the following: my single entry visa to China will be lost as soon as I enter Hong Kong by flight from Shanghai. However, after 2 days in Hong Kong, I plan to go to Kunming and then fly to Myanmar from there (just plan to stay one day in Kunming). I already have my flight ticket to HK and my flight ticket from Kunming to Myanmar. So I guess I can make use of the 144hour permit during my time in Kunming. My question, however, is: can I travel by train from HK to Kunming? If I already have my flight ticket to leave Kunming the day after I arrive? Or is it mandatory in this case to leave HK by flight to Kunming?

Thank you very much in advance for your help.