The boss of Marks & Spencer has told customers the retailer is “working day and night” to manage the cyber attack that has forced it to temporarily shut down its online operations.

Stuart Machin said he was “really sorry” for the disruption to services, but did not say when normal business would resume.

M&S’s problems began over the Easter weekend, with customers reporting problems with Click & Collect and contactless payments.

Last week, the company confirmed it was dealing with a “cyber incident” and paused online orders on its website and apps.

The cyber attack has already had a significant impact on the retailer, with online transactions accounting for about of third of its clothing and home sales. On average, £3.8m is spent on clothing and home products on its website and apps every day.

There are also gaps on the food shelves in some stores as the firm took some of its systems offline as it tries to manage the attack, while its loyalty scheme and gift card payments have been disrupted too.

M&S is not the only retailer to be hit by a cyber attack. This week, both the Co-op and luxury department store Harrods have also been targeted.

Helen Dickinson, chief executive of the British Retail Consortium, told the BBC she was worried about the attacks and acknowledged it was concerning for customers and businesses.

She told BBC Radio 4’s Today programme why big retailers may be vulnerable to such attacks.

“Firstly, they’re obviously high-profile businesses, we all interact with retail each and every day.

“Secondly, they’re highly digital businesses, not just from an online shopping point of view but retailers have lots of systems – payments systems, stock systems.”

But she added that all of the businesses affected at this point had been able to keep their stores open.