About 45 people have had bank cards copied at a service station in the west of the county, a police spokesman said.
Shortly afterwards purchases were made in several overseas countries including Canada, South Africa and Ghana.
Inquiries are continuing and detectives are liaising with the banks and advise customers to check their statements.
Dc Pete Novakovic, of the economic crime unit, said: “These types of incidents, while they are very common up and down the country, are thankfully quite rare in the county.
“People should check their bank statements and also get in touch with their bank who are the lead agency in these cases.
“People should always be cautious. Do not give your card to anyone else and always keep hold of it and put it into the machine yourself.
“If you think there is a camera covering the machine alert the authorities and cover your PIN number with your hand to make sure no-one can read it over your shoulder.”