Specialist officers began a search at Bismark House Mill in Oldham after remains were first discovered by demolition workers on Saturday.
Human remains indicating at least two victims have been recovered from a mill following a fire more than two months ago, police have said.
The force said it received a report last Thursday that four Vietnamese nationals were missing and may have been involved in a fire.
On Wednesday, a force spokesman said the search at the site on Bower Street, where emergency crews were called to a fire on May 7, indicated there were two victims.
Detective Superintendent Lewis Hughes said: “We are carrying out an extensive search of the remnants of the mill to ensure any further human remains are recovered in a way which is respectful to both the deceased and the bereaved.
“Meanwhile, our major incident team are continuing to liaise with partner agencies to ensure potential family members in Vietnam are fully informed and supported.
“Though we’ve now recovered human remains to suggest that at least two people were in the mill during the fire, we remain conscious of the report we received, on Thursday July 21, that four Vietnamese nationals were missing and may have been involved in a fire.
“Alongside the search and recovery efforts, extensive enquiries are being carried out to establish the full circumstances surrounding the fire. Any criminal offences identified as part of this will be progressed immediately and appropriately.
At the time of the blaze, which was extinguished over four days, no-one was believed to have been inside the building, police said.
The incident was referred to the force’s Professional Standards Branch for review due to previous contact relating to the fire and missing persons.
Earlier this week, assistant chief fire officer for Greater Manchester Fire and Rescue Service Leon Parkes said firefighters had followed correct procedures when a decision was made not to enter the mill, due to concerns about the fire and the building’s structural stability.
But, he said there would be a review of the incident and how it was managed.
He said the site was a multi-occupancy warehouse used by a number of companies and was thought to be locked up and closed when the fire broke out in the early hours.
Police asked anyone who is concerned about a missing loved one or who has information about the circumstances surrounding the fire, including activity at the premises before May 7, to contact the Major Incident Room on 0800 051 4675, for UK callers, or (+44) 0207 459 4500, for international callers.
Information can also be submitted via the Major Incident Public Portal at mipp.police.uk or anonymously through Crimestoppers on 0800 555 111.