"We have been notified and making some further inquiries but police are the lead agency on this," said a spokeswoman.
Yesterday workers at the factory revealed they noticed a putrid stench coming from a bale and even handled a limb.
One factory worker in a nearby plant said staff were were "freaked out" when they came across the grisly find.
He posted on social media: "It was next door to my department so yeah staff were freaked out."
Police today had secured a section of the Frankton plant with workers forced to have the day off.
A post mortem investigation was not expected to be completed until later this afternoon, according to police.
Detective Inspector Hywel Jones said the man's identity and age had still not been established.
"In addition to this examination we have a number of enquiries underway seeking to confirm the man's identity. At this stage we are still treating his death as unexplained."
A police spokeswoman also said that reports that the bale of cardboard had been imported were not correct.
A manager at OJI Fibre Solutions referred the New Zealand Herald to the police this morning, but confirmed part of the business was closed today.
A police car could be seen inside a back warehouse, and a second police car was let into the locked area soon after.
Police were also seen door knocking a nearby home.
"At this early stage of the investigation police are still going through the process to identify the body and determine how the body came to be in the bale of cardboard," a police statement said.
In a statement to media, chief executive Jon Ryder said the company will "not be responding to media queries".
"The New Zealand Police have the site locked down at present and we are doing everything we can to help them. At this point in time, it would not be prudent for us to say anything further. We anticipate being able to provide further information later this week."
One worker, who spoke to the Herald on the condition he was not named, said they only knew that "body parts had been found" in the bale of cardboard. Staff were informed earlier in the day about what had happened but had been told not to talk about the incident.
The company used to be Carter Holt Harvey Pulp, Paper and Packaging but was sold to OJI in 2014 and subsequently re-branded.
According to its website, the business employs more than 1850 people in New Zealand.
