Tesco has been hit by hackers, leaving thousands of frustrated shoppers unable to buy groceries online at Britain’s biggest supermarket.

The outage means that its grocery website and app are down for a second day, leaving people unable to book deliveries or amend existing orders.

A Tesco spokesperson said: “Since yesterday, we’ve been experiencing disruption to our online grocery website and app. An attempt was made to interfere with our systems which has caused problems with the search function on the site. We’re working hard to fully restore all services and apologise for the inconvenience.

“There is no reason to believe that this issue impacts customer data and we continue to take ongoing action to make sure all data stays safe.”

Shoppers took to social media to voice their frustration. Some posted messages they had received from the supermarket telling them that because of the “current IT issue” Tesco was unable to access or change any orders at the moment.

Tesco receives 1.3m online orders every week.

Sara Willman, a wholesale seller of flowers to florists in Wiltshire, tweeted: “Yesterday you said to send a DM to cancel my order due today. Today I get a reply to say it’s not possible. I understand you still have IT issues but much as I love gin I don’t need 2 bottles & some crisps this evening, when @asda saved the day with actual food this morning!”

Tesco tweeted on Saturday: “We’re experiencing an issue with our website and app and are working hard to get things back up and running. We apologise for any inconvenience.”

On Sunday morning, the company tweeted: “Our IT teams are doing their best and will have the website and app working as soon as possible. At the moment, we don’t have any updates or a timeframe as to when we can expect this to be. I am really sorry. TY – Cameron”

The rival supermarket Asda stepped in, tweeting: “Hi there, hopefully we can help. We have slots available and some for the same day or tomorrow, if you go to our website or app it will allow you to place an order for items you need :)”