Twenty-one people were rescued after becoming trapped when they fell nine feet as a floor collapsed during a health and safety meeting at a firm.
A meeting was under way when the floor collapsed
A Greater Manchester Fire Service spokesman said a mezzanine floor collapsed at Findel Education in Hyde Buildings, Ashton Road, Hyde.
Firefighters and paramedics used ropes and ladders to free the trapped people.
The fire service said one end of the floor gave way and the people fell 9ft (2.7m) into an empty office.
Eight of those trapped by furniture and supplies were taken to hospital for further treatment.
A fire service spokesman said the person with the worst injury had a suspected broken ankle with others suffering neck, back injuries and bruising.
He said the incident happened during a health and safety meeting.
The Hyde office is the headquarters of Findel Education which is an educational supplies business.
The meeting began at about 1000 GMT on Tuesday with the 21 safety officers sitting around a large wooden conference table.
Staff in the ground floor office underneath noticed the ceiling moving and ran out of the room seconds before it collapsed.
More health and safety officers arrived later from Tameside Borough Council to investigate the cause of the incident.
A spokesman for Findel Education Ltd said: "The affected area has been sealed off but the rest of the building remains operational, in agreement with the health and safety officers."