The body of another worker caught up in Friday's fire at Wood Flour Mills, near Macclesfield, was found on Sunday.
All four were believed to be working in the upper floors of the mill on Friday when an explosion and fire reduced the four-storey building to rubble.
Firefighters have warned it may "take a long time" to complete the search.
A search team is excavating the 5m x 5m (16ft x 16ft) area where the body - which has not yet been identified - was found.
The families of Derek Moore, 62, Dorothy Bailey, 62, Jason Shingler, 38, and William Barks, 51, were all informed when the body was found, and continue to be updated and supported by police officers.
Another woman is in hospital with serious but not life-threatening injuries.
Two other men remain in hospital in a stable condition and another man has been discharged with minor injuries.
In a statement, the site owner - Wood Treatment Ltd - said it was "shocked and saddened" by the blast in Bosley.
The police are conducting a joint investigation with the Health and Safety Executive (HSE).
The site, which manufactures wood flour used for making laminate flooring, was also struck by fires in 2010 and 2012.
The search and recovery mission to find three people still missing after an explosion at a Cheshire wood processing plant has entered a fifth day.