Nineteen people have been injured in a ferry accident in Sydney, with one suffering spinal injuries.

NSW Ambulance Inspector Norm Spalding said about 4:20pm emergency services received numerous calls about a collision between a ferry and a jetty at Circular Quay.

"On arrival we found a number of people, many of them tourists [of] non-English speaking background, who had varying injuries, from suspected spinal injuries right to lumps and bumps, abrasions, what have you," Inspector Spalding said.

"We've assessed and treated a total of 19 patients.

"We have transported a total of six patients to St Vincent's and Sydney Hospitals and all patients would be classified as being in a stable condition."

Man thrown to ground on upper deck

Inspector Spalding said the man who suffered the spinal injury was on the upper deck of the ferry when the crash occurred.

"He was thrown to the ground, striking his back on the bulk head," he said.

Inspector Spalding said the incident could have been much worse. ( ABC News )

"He was treated as a spinal patient as a precaution, but I would be hopeful that everything would be OK with him.

"It was necessary to get Police Rescue to assist us to extricate the patient from the upper deck of the ferry."

He said a woman who suffered leg and arm injuries was taken away on a stretcher, but all the other patients were assisted and taken to hospital sitting in ambulances.

Inspector Spalding said the injuries could have been much worse.

"It was a good outcome for everybody," he said.

Accident caused 'very loud crash'

Darryl McGregor, a visually impaired busker, was nearby when the accident happened.

"I heard this very loud crash and I was informed very quickly by another bystander that a ferry had hit the bollard there which is a protection against the jetty.

"And yes it was very loud."

Darryl McGregor said he heard a loud noise when the ferry crashed into the jetty. ( ABC News )

He said he had not heard of anything like this happening before.

"I don't know whether this was mechanical ... I assume so."

Two ferry services have been cancelled: the 545 from Circular Quay to Mosman (Taronga Zoo) ferry and the 601 from Mosman (Taronga Zoo) to Circular Quay.

A NSW Transport spokesman said a Sydney Ferries Supercat came into contact with the far eastern pontoon on Circular Quay Wharf as it was berthing this afternoon.

"The vessel was operating the 3:45pm Watsons Bay to Circular Quay service," he said.

The spokesman said the Office of Transport Safety Investigations (OTSI) was investigating the incident.

"Transport for NSW is working with Sydney Ferries operator Harbour City Ferries and will fully cooperate with OTSI to identify the cause of the incident," he said.