Getting a Mainland China Visa in HKG

We have a single entry China Visa from India. Need to go to HKG from Guangzhou (GZ) and come back to take return flight from GZ.
It seems once we go out of GZ (to HKG) we can't re-enter China.
Is there a way we get a short (just about 48 hour maybe) visa for China from HKG? Our flights are booked and we have to be back in GZ for return flight.