My experience in Beijing is that there are 2 transit enterances but I have only seen one operating at a time, so you may think it is closed but you need to walk to the other side of the immigration area. The visa on entry is the next desk then its the main immigration. There can be issues if the transit station for boarding passes is not open for your flight then you cannot transit. I was actually kicked out and made to enter China when I arrived late one night and they told me that I had to book in at the counter next morning for the boarding pass. In this case I didnt proceed through visa on entry they just stamped and put me through.