Some Tesco customers are reporting not being able to access the retailer's app and website.
People have taken to social media to complain about problems checking-out online shopping and with accessing their Clubcards through Tesco's app.
Tesco's account on X replied to one user saying it is having "intermittent system issues at the moment which the IT team are currently working hard to resolve."
The BBC has contacted Tesco for comment.
Customers on social media have listed multiple problems. One reports issues with Apple Pay in a Tesco store as well as difficulties with gift cards.
Many describe being unable to process changes to online orders.
Outage monitoring site Downdetector is showing increasing levels of reported problems with Tesco's website.
Two other major retailers Marks and Spencer (M&S) and the Co-op have suffered massive disruption in recent weeks, in their cases due to cyber attacks.
It is not known if the problems being experienced by Tesco are related to a hack or are the result of internal IT issues.
The supermarket chain - the UK's biggest - said in early 2024 that its Clubcard loyalty scheme, offering shoppers discounts on products in-store and online, had more than 20m members.
One social media user said on X they had been encountering issues with the supermarket's app and website for about four hours.
Tesco told them in a reply that the services were experiencing "technical issues" and asked them to "try again later".
Others have said they were unable to pull up their Clubcard on their Tesco app to collect points or use vouchers while shopping.