'Coffee kindness' plot sweeps through city

Patrons of coffee shops in a US city have been purchasing beverages for strangers in a new kindness movement.

Starbucks customers have been anonymously picking up the tabs of fellow visitors under the optional scheme, which is becoming increasingly popular in Birmingham, Alabama.

The movement originates back to 2000, when Catherine Ryan Hyde encouraged random acts of kindness in her book Pay It Forward.

A Starbucks spokeswoman explained that the idea's recent popularity is "consumer-driven", adding that most customers decide to continue the trend if they are rewarded themselves.

One patron, Sharon Dierking, first discovered the scheme when she tried to pay for a coffee and was informed that a man had already settled her bill.

She told The Birmingham News: "I was completely dumbfounded, but I was thrilled."

Confirming that she passed on the kindness a few days later, Dierking added: "It makes you feel good and it brightens your day."