Police said the detective in charge of the investigate would hold a press conference this morning.
A post-mortem examination was done in Auckland yesterday after a worker found human body parts about 11am on Tuesday.
The section of the factory on Pukeko St was immediately closed down, and police cars and officers were at the plant yesterday.
Oji and police said they would not answer questions while the investigation was under way.
However, police did reveal that the bale was not imported.
The Herald also understands workers were told yesterday that multiple body parts were found in the bales of cardboard on Tuesday morning.
Factory workers first uncovered a leg, and arms and the rest of the body were found among the bales of recycled cardboard, according to sources.
Staff working in the area of the factory where the body was found, understood to be the recycling area, were not at work yesterday.
The Herald understands other Oji Fibre Solutions plants, including its biggest, the Kinleith Mill in Tokoroa, have been closed for fear of products being contaminated. Products have also been recalled for the same reason.
Workers did not believe the body was a staff member.
The company, which used to be Carter Holt Harvey Pulp, Paper and Packaging and was sold to Oji in 2014, received cardboard products from waste management services in Hamilton.
It also has its own service, Full Circle, for collecting recycling products.
Hamilton City Council waters manager Andrew Parsons said the council contracted Waste Management NZ to collect its recycling and that products were taken to Oji for processing.
"We understand Waste Management is one of a number of companies which supplies cardboard and paper to the Oji plant in Hamilton."
A Waste Management spokeswoman said the company had "nothing to do" with the incident.
EnviroWaste Hamilton did not return calls last night.