A man hit and dragged by a bus in Sydney's CBD has been taken to hospital in a critical condition with serious injuries.


Emergency services were called to the corner of George and Bridge Streets about 6.50pm (AEDT) on Friday after receiving reports that a pedestrian had been struck by a bus.


"It is believed a coach was travelling south along George Street when it turned into Bridge Street and struck the man as he attempted to cross the road," police said in a statement.


A CareFlight spokesman told AAP the man was dragged several metres down the road by the bus before becoming trapped in the wheel arch.


The 30-year-old Hurstville man was put on full life support and taken to St Vincent's Hospital with serious leg, chest and pelvis injuries, the spokesman said.


No passengers were aboard the bus at the time.


The driver has been taken to Sydney Hospital for mandatory blood and urine tests.


While police investigate the incident, the two eastbound lanes of Bridge Street will remain closed.


Anyone with information is asked to contact Crime Stoppers on 1800 333 000.


AAP