Nottinghamshire Police "is not yet sufficiently prepared to tackle child sexual exploitation", according to its latest inspection report.
The HMIC rated Nottinghamshire Police to be 'good' overall in its effectiveness review but detailed analysis said that it requires improvement in dealing with vulnerable victims, including children.
It's report said: "When frontline officers identify a victim is vulnerable, they generally provide good safeguarding for the victim, however, we sometimes found confusion as to whether a risk assessment or a child referral needs to take place.
"We also found backlogs in assessments, some involving children, awaiting referral to other organisations.
"The force has improved its approach to tackling domestic abuse but still has work to do.
"In addition, it has decided not to refer all cases assessed as high risk to multi-agency risk assessment conferences.
"The force responds well to missing and absent children, however, it is not yet sufficiently prepared to tackle child sexual exploitation."
The force is increasing the number of specialist staff to deal with vulnerable victims, but the report says workloads are still too high.
It adds that only "limited training" has been provided to staff on domestic abuse, missing and absent children and child sexual exploitation.
The NSPCC said the report's findings were "deeply disturbing".
A spokesman said: "It's deeply disturbing that Nottinghamshire Police has not been not tackling child sexual exploitation effectively.
"And we are concerned that the force was deemed in need of improvement in the way it protects some of the most vulnerable members of its community from harm.
"We welcome plans to increase the number of staff in specialist units to ensure investigators provide tailored support to victims who are most at risk.
"However we are concerned the HMIC found confusion among frontline officers about the correct paperwork despite guidance being available.
"As more victims of child abuse and exploitation continue to come forward, it's essential that all the police are properly trained and equipped to respond to these most horrific of crimes."
But on an Ofsted-style rating scheme in four categories, supporting vulnerable victims was the only one that required improvement according to inspectors.
Nottinghamshire Police was rated good at dealing with organised crime, investigating crime and managing offences and preventing anti-social behaviour and keeping people safe.
Deputy Chief Constable Sue Fish said: "There has been some outstanding work undertaken across the force to reduce crime, tackle serious and organised crime and protect the public.
"The introduction of mental health triage cars, staffed by a police officer and a mental health professional, means that people are offered the right support at the first point of contact, rather than being taken into custody. Since April last year, we have also had no children with mental health issues in our cells.
"Our officers and staff work hard to prevent crime, detect crime and keep people safe, and we have strong links with our partners. It is important to recognise there is strength in working together to understand local issues and resolve them."
Her majesty's inspector Zoe Billingham said: "In this very broad inspection covering some of the most important areas of operational policing, HMIC has judged Nottinghamshire Police to be good at keeping people safe and reducing crime."
