Gardaí in the town yesterday appealed to anyone who used the Bank of Ireland banklink at Market Cross in the past month to check their accounts.
On discovering that cash had been withdrawn from their accounts, several customers reported the thefts to the gardaí in recent days.
The affected customers then cancelled their cards.
A Garda spokesman said they had not yet quantified how many accounts had been targeted.
“Reports are still coming in from customers and we expect more to arrive as people gradually learn money has been withdrawn from their accounts,” her said.
A skimming machine, which was found on the bank link machine, is being forensically examined.
ATMs in other parts of Killarney have been hit in the past few years.
Meanwhile, latest Garda statistics show a sharp fall in the number of thefts from shops in Tralee last year, down from 134 to 93.
Thefts of tools and other property, however, rose from 112 to 174.
Supt Pat Sullivan of Tralee said people had been warned to lock up tools and to close windows when their properties were not occupied but this was still happening, he said.