Should i apply for visa now to enter china for 4 days as would like to go sight seeing 4 days?

I will be in hong kong in april for 9 days 21st to 29th on a returning trip from the states me and my partner both have Australia passports while there if its possible to go for a tour in china this part of our trip was totally unplanned i have just gotten some quotes about a 4 day tour from Hong Kong to Beijing to see the sights just wondering what the best way to tackle this as i havent booked the tour or the flights reading some of the comments what would be the best soloution