An elderly woman has been hospitalised after she was trapped underneath a bus in Bondi Junction on Thursday morning.

A NSW Ambulance spokeswoman said the woman, who is believed to be in her 70s or 80s, was hit by a bus at the bus interchange near the corner of Grafton and Grosvenor streets about 11am.

It took paramedics 12 minutes to free the woman because her legs were stuck beneath the bus, the spokeswoman said.

She was taken to St Vincent Hospital in a serious condition suffering head and leg injuries.

The male bus driver was also taken to hospital for mandatory blood and urine testing. Police said they will investigate the incident.