Police said a “small number” of people had been scammed out of £1.2 million in the north-east area.
Detective Inspector Iain McPhail, of the economic crime and financial investigation unit, said people have had their “hard-earned savings wiped out in minutes”.
He said: “Scams like these are completely sickening, with the criminal at the other end of the phone having no regard for their victim and the devastation their actions will cause.
“Pension pots and retirement funds can be stolen within a matter of minutes, with hard-earned savings wiped out without warning.
“Sadly, the victims deliberately targeted in these cases are often older or someone that’s perceived to be more vulnerable.
“They prey on people’s good nature and use scare tactics. It is cruel, it is callous and it is beyond comprehension.
“In these most recent cases, the callers have pretended to be from their victim’s bank saying they are investigating fraudulent activity by staff within the organisation.
“They ask their victim to move substantial amounts of money into foreign accounts for safe-keeping and request that they do not report the call for fear of ruining the investigation.
“The fraudsters also induce the victims to attend their own bank or building society personally to transfer the money abroad, providing the cover story that it is for some form of international investment.”
He added: “Often, people who fall victim to this type of scam feel foolish as they think it will never happen to them, however these criminals know what tactics to use to force you into acting in a way you never imagine you could.
“At times these people have had daily contact with their victims a period of weeks to enhance their credibility and encourage the victims to carry out the transactions. Banks will never do this.”
Anyone with concerns about scam calls should call police on 101.