Tills broke down at Tesco this morning after an overnight software update caused problems with the system.
Customers in some shops could only use the self-service tills after the Sunday-night update caused many of the main tills to go down.
IT staff are currently working on the problem and a spokesman said the tills are starting to come back up.
The glitch affected stores around the country. Tesco says it does not know what caused the problem but said the work that caused it was "routine".
A spokesman said, "A number of stores were affected by a routine IT upgrade this morning at various locations in the country. Our experts are fixing the problem as we speak in the meantime we are very sorry for the delay and thank customers for their patience."