A woman has had emergency surgery after being pinned under a bus for two hours in Sydney's city centre.
Emergency services described the extraction of the woman from underneath a city bus on Wednesday as one of the most delicate rescues in almost 40 years.
The woman was struck by the bus and became trapped in its axles at the intersection of Clarence Street and Erskine Street just before 4pm (AEDT).
She spent two hours pinned under the vehicle before a rescue team could free her.
She was rushed to the Royal North Shore Hospital.
A hospital spokeswoman said the woman, 51, remained in critical condition on Wednesday night.
A police spokeswoman said the woman had undergone emergency surgery.
Ambulance Inspector Norm Spalding said the rescue was "slow, arduous and very difficult for all those involved".
"In 37 years I would say this would be in the top five or six cases that I have been involved in in terms of delicacy," he said.
Insp Spalding said the woman had extensive injuries to her lower limbs.
She was conscious for much of the joint rescue operation by NSW ambulance, police and fire service crews.
A broken blue lunch box and a lone shoe were left on the usually busy Clarence Street, metres from where the woman was trapped under the bus.
Victor Guo was working nearby at Pie Face when he heard the woman's screams.
"The screams lasted for five to 10 minutes and suddenly stopped," he told AAP.
"I think the bus has hit the girl and pulled her to the front of my shop ... about 30 or 40 metres."
Paramedics first on the scene held the woman's hand, as a specialist medical team landed in a helicopter at nearby Barangaroo to lend help.