The woman had been standing at a bus stop in Kidderminster next to an academy site when the 6ft by 7ft metal panel hit her, reports the Express & Star.
The £6.1 million education and training centre is being created in the Piano Building, a former carpet warehouse, for Kidderminster College and Birmingham Metropolitan College. Main contractor for the project is local firm Thomas Vale.
Passers-by helped pull the metal hoarding from the woman so paramedics were able to treat her when they arrived at the scene. An air ambulance took her to the Queen Elizabeth Hospital, in Birmingham.
West Midlands Ambulance Service today the injury was “serious”.
West Mercia Police said officers had taken statements from witnesses and the matter had now been handed to the Health and Safety Executive, who would be investigating.
Police spokesman Dylan Evans said: “A woman had been standing near to the bus stop when fencing around a construction site had come loose. She had been assisted by members of the public who helped get the metal off her.”
He said it was not known what had caused the fencing to come loose, although it happened during windy weather.