90 day multiple enter visa for tourism

My wife and I are retired Australians who are travelling in Asia. We are currently in Bangkok and are planning to travel (fly) to Hong Kong for a short stay. Thenwe would like to catch a train to Beijing for a one week visit. From there we wish to travel to Mongolia for a month then re-enter China to travel by train and bus to Urumqi and Kashgar Can we apply for a 90 day multiple enter visa for our time in China. From Kashgar we will travel to Tajikistan. Please advise.

Yours Faithfully - Phil