The desperate measures follow Prime Minister Alexis Tsipras' weekend decision to call a referendum on creditor proposals for Greek reforms in return for vital bailout funds.

With national newspapers splashing front pages with photos of long queues outside cash machines and petrol stations, the Government acted to close all banks at least until after July 5, the date of the referendum, and shut down all cash machines for 24 hours. ATMs will re-open this afternoon with a EUR60 daily withdrawal limit applied. Withdrawals by card-carrying tourists will not have the limits applied.

Greeks will still be able to pay bills online using Web banking, but will not be able to move money to accounts abroad.

In making its decision to suspend operations in Greece, Western Union says it had not seen a significant increase in customers moving money out of the country, rather a rise in inbound transferrals.

"Our inbound business is seeing an upswing and we will continue to monitor this closely as and when our business in Greece is operational once gain," the company said in a statement emailed to Reuters on Monday.