The company's Web site went offline for around one hour while customers also experienced connectivity issues with the Square app.

Despite sharing a founder - Jack Dorsey - with Twitter, the firm has not used the microblogging site to communicate with users but a spokesman has confirmed to tech site The Next Web that "some payments could not be processed".

The outage comes only a fortnight after Square secured a massive deal with Starbucks that will soon see its systems take the strain of processing all card payments for the coffee chain giant.