transit visa in Guangzhou is needed?

Hi !
We are a Spanish couple living in Dubai, and we are flying from Dubai to Cambodia through Guangzhou (China) in 10 days. We will stay in the Guangzou airport for 7 hours. If we stay in the Guangzhou airport, do we need a transit visa ? If so, is it possible to get the transit visa upon arrival or we have to apply for the visa in advance? Thanks for the information!!!
Sonia