Police were called to calm crowds that gathered after a cash machine started dispensing "free money".
The cash machine at the Nacton Road Lloyds TSB in Ipswich began issuing twice the requested amount at about 8pm on Thursday.
Arguments broke out among those trying to use the faulty machine and police were called to keep watch until staff could put the problem right.
It is thought about 30 people benefited from the fault - and it is unlikely the bank will be able to trace them to reclaim the money.
Emma Hutchinson, from Ipswich, told the Ipswich Star: "Word got around pretty quickly. My friend asked for £40 and the machine gave out £80."
She went to see if the rumour was true but decided not to withdraw any money herself.
A Suffolk Police spokesman said: "The incorrect dispensing of cash is not a police issue, but we remained on scene until staff from the Lloyds bank arrived and turned off the cash machine."
A spokesman for Lloyds TSB said: "For a very short period of time, the ATM at Nacton Road was misdispensing cash whilst the branch was closed.
"The machine was put out of service. We apologise for any inconvenience caused."Suggest a correction