Some nationalities, 54 in total, including Aussies, can get a 144 hour visa free exemption on arrival and then you will be limited to a certain area to visit. For example, if you fly into Shanghai, you can visit Shanghai, Zhejiang and maybe Jiangsu (cannot remember offhand). However, you cannot fly back to Thailand directly. You need to fly to a third country, then Thailand. You really need to check a Chinese visa website to make sure there have not been any changes to these rules