Transiting hrough bejing on Pakistani passport.

Hi!
I am zeeshan living in australia on student visa holding pakistan passport. I have my flight going through bejing on my way to pakistan. I have around 15 hours one side and then 20 hours on my way back to australia time layover at bejing internationals airport. Do i need any transit visa for even transiting through bejing being pakistani national.
What if i need to leave airport for few hours during my stay. Is there any visa free stay i can enjoy with for few hours.
Answer is much apprecieted. Thanks