Transit Visa at Shenzhen Bao'an Airport

I have US passport. Arriving at SZX with Air Asia flight AK122 and leaving to LAX on Air China flight CA769 after aprox. 4 hrs. I have to go to Air China counter to get my boarding pass from SZX to LAX. I guess I have to go outside the custom area. Do I need get a visa before I arrive? Will I get be able to go to Air China counter with out visa or they will give me visa at the airport?