Do I need a double entry visa while transiting through China.

Hello,
I'm travelling from Sydney to Rome via Shenzhen and Wuhan with China southern. With a transit time in China of approximately 8 hrs. Then returning to Sydney 4 weeks later via Wuhan and Shenzhen, with a transit time in China of approximately 10 hours. I was under the impression that I could enjoy 24hr free transit in both directions. But now my travel agent is saying that I need a double entry visa because I am transiting through China in both directions. Can anybody clarify this?
Cheers Paul.