Tesco’s website and app are up and running again after a hack, which left thousands of customers unable to shop online at the weekend.

The outage, which meant customers were unable to unable to book deliveries or amend existing orders, began on Saturday morning and continued into Sunday.

A spokesperson said on Sunday night: “Our online grocery website and app are now back up and running. Our teams have worked around the clock to restore service, and we’re really sorry to our customers for the inconvenience caused.”

Britain’s biggest supermarket chain said the problem was because of an attempt to interfere with its systems, but added there was no reason to believe customer data was affected.

Customers were told they may need to enter a virtual waiting room before accessing the site as Tesco tries to manage the initial flow of traffic.

The planned measure is regularly used at peak shopping times to ensure customers have a smooth experience on the site, the company added.

The outage prompted a flood of queries to Tesco over the weekend, and many customers voiced their frustration on Twitter. The supermarket receives 1.3m online orders every week.

Tesco was previously hacked in 2014, when it was forced to suspend online customer accounts after the details of more than 2,000, including passwords, were posted online. A separate attack on Tesco’s banking arm resulted in the loss of £2.5m two years later.

The number of cyber-attacks around the world has soared in recent years, with many companies and other organisations targeted.