Three hospitalised after Sydney CBD crash

Two people have suffered serious injuries and a third person has been hurt in a crash between a bus and a van in Sydney's CBD, police say.

Emergency services were called to Park Street just before 4pm on Thursday, including a rescue helicopter to treat the patients following the crash between the van and bus, believed to be empty of passengers.

Two people with severe leg injuries have been taken to St Vincent's Hospital and a third person has been taken to Sydney Hospital in a stable condition.

Early investigations suggest the bus hit the back of the van, which was being unloaded by three men, police say.

The two men injured had been standing at the back of the van.

One eyewitness said the black van was parked in a bus lane and one of the men was knocked unconscious for about 15 minutes after he was hit.

"He was getting something out (of the back of the van) but I don't know what but he just got unlucky. Very unlucky," local worker Sam Rumba said.