The unnamed 23-year suffered undisclosed injuries but Greater Manchester Police said he was in a critical but stable condition.
The police said: “At around 10.40am on Wednesday 12 March 2014, police were called to Premier Foods on Cale Lane, Wigan following a report that a piece of machinery had fallen on top of a man.”
Officers and emergency services attended, and an Air Ambulance was called. The man was air-lifted to the Royal Preston Hospital.
A spokesperson for the Health and Safety Executive (HSE) said that a full investigation had been launched, with inspectors visiting the site.