Greater Manchester Police says 'technical difficulties' are preventing staff from answering non-emergency calls this morning (Monday).
The force reported the problem via Twitter just after 8.30am on Monday morning (December 21).
The message warned that those who need to contact police should use the reporting facilities on GMP’s website.
People are still being urged to call 999 in an emergency.
The force said the technical problems are affecting systems at force headquarters, including calls coming into the Operational Communications Branch.
Asked if the problem affected the entire IOPS system, which has given GMP a headache since being installed, the force said: "This issue does affect our Control Works system, but early indications are that it is a network issue.
"There is a BT engineer currently working to resolve the problem and we hope to have the matter resolved swiftly."
Greater Manchester Police earlier tweeted: “We're currently experiencing some technical difficulties which means we may not be able to answer non-emergency calls.
“If you need to contact us about something please use the reporting facilities on our website https://crowd.in/6Nhbd0.
“Please call 999 in an emergency.”
A GMP spokesperson said: "We are currently experiencing technical issues which are affecting systems at Force HQ, including calls coming into our Operational Communications Branch, so we are advising the public to make non-emergency reports online via our website and not call 101.
"We have rigorously tested business continuity plans in place to prepare us for circumstances such as this so the issue should not impact our response to emergency incidents. We would therefore continue to encourage members of the public to only call 999 in an emergency.
"We are currently investigating the cause of the issue and hope to have this matter resolved swiftly."
Last week, GMP's troubled new computer system iOPS crashed again.
Call handlers were forced to take details of crime reports on paper on Wednesday afternoon when a number of the force's computer systems, including iOPS, suddenly failed at about 1.30pm.
Bosses initially feared a power outage at a GMP building was the cause - but engineers quickly realised it was an IT failure.
All systems were eventually restored after two hours.
The IT crash resulted in 999 and non-emergency calls being taken down on paper, force bosses confirmed.
GMP said 'tried and tested business continuity plans were activated, which ensured that service delivery to our communities was minimised'.
The force has been dogged by problems since it introduced its Integrated Operational Policing System (iOPS) at a cost of £27m in July last year, some 19 months behind schedule.
Her Majesty’s Inspectorate of Constabulary (HMIC) told the force earlier this year that issues with the IT system had exposed hundreds of vulnerable people to 'potential risk of harm'.
Chief Constable Ian Hopkins announced his resignation on Friday after his force was placed in special measures due to concerns over its failure to record more than 80,000 crimes in the space of a year.
HMIC said it was left 'deeply troubled' over how cases handled by GMP were closed without proper investigation.
Greater Manchester mayor Andy Burnham said his job of holding Mr Hopkins and his force to account had been 'made difficult' by an 'overly defensive culture within GMP'.
