The London Evening Standard reported that the young woman was hit by the frame as workmen installed windows at a new office block on Hanover Square.
According to eyewitness reports, the frame had been propped up against a wall and fell on the woman as she walked past.
An eyewitness told the Standard that he’d seen similar frames lifted by cranes yesterday, indicating how heavy they were.
Police cars and ambulances rushed to the scene and paramedics fought to save her as she lay in the square, it is reported.
The BBC said that the office block, 5 Hanover Square, is a multi-million pound development and that the ground floor is being turned into an art gallery.
A Met Police spokesman told the Standard: “We were called to Hanover Square with the junction of Hanover Street at 1130am by London Ambulance Service. At this stage it is believed an unknown object has fallen from a building and struck a female on the street.
“She was treated by medics but pronounced dead at the scene. The Health and Safety Executive (HSE) is aware. Inquiries are ongoing.”