A homeless man is fighting for his life after being crushed by a rubbish truck this morning.

The man, 30, was hit by a reversing rubbish truck in Degraves Street in the CBD at around 5.10am.

He was taken to The Royal Melbourne Hospital in a critical condition.

Police say the man may have been sleeping across the footpath and road when the accident occurred.

The driver of the rubbish truck stopped to help and is assisting police with their inquiries.

Investigators are calling for anyone who may have seen the man in the laneway prior to the incident, or who witnessed the accident itself, to come forward.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at crimestoppersvic.com.au