Human remains have been discovered at a recycling centre with forensic officers still working on site.
Police were called to the plant at Tofts Farm Industrial Estate in Hartlepool on Sunday after employees found a number of bones.
Following examination by specialists, they were confirmed as human.
Cleveland Police said the investigation was “extremely complex and sensitive due to the circumstances in which the remains were found”.
Det Insp Chris Pringle said: “I understand how concerning this will be for those living within our community and the wider public.”
Det Insp Pringle said a team of detectives and officers from departments across the force were “working at pace” to identify the remains as fast as possible.
“However, this will take a considerable amount of time,” he said.
“I know there will be families who have missing loved ones and worried about the remains and I want to reassure you that, if any relevant information comes to light, we will be in touch.”
The plant – run by Biffa – has been closed since the discovery was made, with a police cordon in place.
A spokesperson confirmed the site would remain closed until further notice but said the company was unable to comment on the investigation.