Nanjing stop over, visiting whitout Chinese visa

We have transit in Nanjing and a stop over of 6.5H (Hong Kong - Nanjing - Sydney), are we allowed to visit the city without a Chinese mainland entry permit? (Finnish nationality). We will have visa to AUS and flight tickets aswell when arriving to Nanjing. I was checking the Chinese embassy site, and Nanjing airport was not mentioned there.