Do I need a transit visa? Transit at Baiyun International Airport

I'm a Vietnamese student. I study in Seoul and want to come back my country in next month. So, I buy a transit ticket to fly from Seoul to HoChiMinh via Guǎngzhōu. I'll stay there 9 hours and I want to go out to try the Chinese cultural. Do I need a visa application in this case?
Some friends of mine transited at Beijing Airport at this February. They go out about 8 hours and they don't need a visa application before. When they arrived Beijing, they get a stamp for transit in 24 hours and they go out the airport easily. So they suggest me not apply for visa before the flight. I don't know what should I do ?
Help me, please ^^