Would it be possible to obtain a visa to visit china for 1 day?

You needn't apply one for HK because you have 30 days visa-free period there. For mainland China, you can apply for a L type before you go to HK. You should prepare your passport, completed application form, a recent passport size photo and the invitation letter. If you don't have the invitation letter, you need to submit your round-trip air tickets and hotel booking in mainland China.