A watchdog said it has "significant concerns" after people were left in urine-soaked beds at a care home.
The Care Quality Commission (CQC) said Werrington Lodge in Peterborough was "unclean" and failed to protect its residents from the risk of infection.
Cambridgeshire Police said it started an investigation at the home last month following agencies' concerns.
Owner Barchester Healthcare said "immediate action" had been taken to address problems.
The CQC, which monitors healthcare standards in England, inspected the care home over five days in May.
It said some people had lost weight and had dry mouths, with staff not supporting them to maintain their nutrition.
Inspectors said some staff showed a lack of compassion, with calls for help from residents being ignored.
Areas of the home also "smelled of urine" with "dirty carpets and furniture", the CQC said.
It blamed a lack of leadership, with the manager and nurses not properly directing staff.
As a result, the CQC made immediate referrals to Peterborough City Council's safeguarding vulnerable adults team and served eight warning notices on Barchester Healthcare.
Following another inspection in June, two notices were lifted, but six still remain.
A Werrington Lodge spokeswoman said it had taken "immediate action" as it was "deeply concerned" the home was below standards.
She added the home had since employed more staff and invested in training.
Cambridgeshire Police said after referrals from partner agencies it had begun an investigation, adding: "We have written to the families of residents at the home to make them aware of the investigation and given them details of who to contact should they have any concerns."
Peterborough City Council said an action plan had been agreed with the home and it would monitor it to ensure standards were being met.
It said none of the 70 residents that it funded had been moved out, but some had left of their own accord.