West Mercia Police said it was aware of criminals pretending to be police officers and bank staff, and that victims had handed over thousands of pounds over the last few days.
Elderly and vulnerable people have been the priority target.
Detective Inspector Emma Wright said: "Sadly, these predators are again targeting vulnerable people who are being fooled into believing their bank accounts have been compromised. These victims may not have seen the news recently or be aware of media and police reports about this scam.
“I urge everyone who has elderly or vulnerable relatives to please give them call, call over the fence to their neighbour or remind them if they pop into your shop that the police will never, ever, call you and instruct you to withdraw your cash.
"No officer will ever ask for you to travel to a bank and hand over your money as part of an investigation, if a loved one is in custody or if your account has been compromised.
"One method used to ensure a victim paid a criminal was that there was an open case on them and they needed to pay nearly £1,000 or they would be arrested.
“Everyone should also remember that no bank or government agency will ever contact you and request you disclose personal or financial information or demand that you partake in any activity to support an ongoing investigation of theirs. This tactic, similar to the fake police officer method has left one victim losing more than £250,000 last week.
“These criminals are significant members of organised crime gangs with the confidence and the experience to be very convincing and ‘Courier Fraud’ is just one element of their criminal activities. But we can defeat them in one simple act: hanging up the phone. No police officer will telephone your granny, your dad or you and ask for your money. They are lying, they are criminals and you can beat them by ending the call."