When applying for a China Visa, do I simply turn up on the day and queue for the application, or do I have to make an appointment?

Also, I'm currently in the USA and have been told that I can't apply for a visa to China from the USA China embassy because my date of travel is after my US visa expires. Is there any other way I can apply for a visa to China from the US? I would be travelling to China from Singapore, but I am afraid that I will not be home long enough to apply for a visa.