The woman has been taken to hospital after the incident, which happened on the M60 at about 9am.
Drivers heading in that direction from Leeds or Huddersfield have been warned to expect delays.
Police said: "UPDATE: M60 reopened. Officers were responding to reports of woman fallen from bridge near to M60 junc 27. She has been taken to hospital"
The woman's condition is not yet known.
Do you know anyone driving in that direction?