Police say the 21-year-old rider was trapped under the truck for some time.
A Westpac Rescue Helicopter transported the rider to John Hunter Hospital in a serious, but stable condition.
We offer our sincere best wishes for a speedy recovery.
The male driver of the truck has been taken to hospital for mandatory testing.
Two of three southbound lanes on Maitland Road were closed. For the latest traffic updates, visit www.livetraffic.com.
Anyone with information about this incident is urged to contact Crime Stoppers: 1800 333 000 or https://nsw.crimestoppers.com.au. Information is treated in strict confidence. The public is reminded not to report crime via NSW Police social media pages.
It is still not yet known what caused these crashes and we do not assume any blame.
Riders should always exercise extreme caution when riding around trucks, especially in heavy traffic.
Trucks have a lot of blind spots and motorcycles can easily disappear from their view.