Do I need an Visa?

I'm a Vietnamese citizen and I'll fly from Frankfurt to Hanoi with China Southern. I have a stopover in Guangzhou but there's a technical stop in Changsha. Do I need entry permit, because I stop in Changsha first and then continue to fly to Guangzhou with the same plane? Nobody can give me a clear answer - even the chinese council. My stay in Guangzhou will take 3 hours and I won't leave the airport.