Santander says the hole-in-the-wall dispensers were closed immediately when it discovered “potential criminal activity and vandalism.”
The bank has not identified which machines have been the subject of suspicious activity, although one is thought to be in Clifton Street, Lytham.
Police investigating possible fraud say criminals have been targeting machines in an attempt to steal card details and cash. Officers revealed a range of devices may have been used.
A spokesman for Lancashire Constabulary said all cash machine users across the county should be vigilant, not just those using Santander.
“The advice is not limited to a specific area or town,” said the spokesman.
“We are advising the public to be vigilant, in particular of Santander machines, but of any cash machines.
“Report anything suspicious, have a visual check of the cash point and if in doubt leave it and go somewhere else.”
The force issued a message on Twitter saying: “Security at Santander ATMs in Lancs has been compromised. Advice is not to use them. If you have lost money please contact the bank and 101.”
Cheshire Police have also issued an alert after suspicious behaviour at ATMs in their area.
Santander said in Lancashire “five ATMs were shut down immediately,” but cash machines elsewhere remained “fully operational”.
People who have lost money have been urged to contact the bank and police.