With Direct transit (24h visa exemption), is it allowed to leave the airport?

Hi, I will transit through Guangzhou international airport with about 15 hour layover time. I hold a Vietnamese passport. As far as I understand, I'm qualified for the 24 hour Direct Transit. My question is, during this 24 hours, am I allowed to leave the airport? And, is it allowed to go to Shenzhen, which is inside Guangdong province? Thanks.