Victims have been contacted by scammers claiming to be from the police or banks about alleged fraudulent activity connected to their accounts.
The crooks have picked up cards and PIN numbers from several victims which they have then used to buy gold jewellery in Huddersfield, Bradford and Manchester.
One victim, from Bradford, also had a £40,000 loan taken out in their name.
PC Toni Hinnells, from Bradford CID, said: “The police or banking staff would never ask someone for their banking details or call someone to speak about suspected fraudulent activity on their bank account.
“If you receive one of these calls and you’re still not sure whether it’s genuine, put the phone down and contact your bank separately. They should be able to confirm if they are aware of any suspected fraud with your account.
“I would advise people not to disclose their personal details online and to make sure that any personal banking documentation is shredded before being thrown away.”
Police have issued descriptions of two Asian men, who called at a Bradford address to collect banking details.
One is described as being about 5ft 10ins tall and slim. He is believed to be in his early 30s and was smartly dressed and clean shaven, with short, dark spikey hair.
The second man is believed to be aged between 30 and 35. He is of medium build with a fair complexion and had chin-length long dark hair, cut in a bob.
Anyone with information should call Action Fraud on 0300 1232040.