A Pak 'n Save Wainoni shopper who won $3.8 million with a ticket from the store wandered around with nothing in his trolley for an hour after finding out he won. (File photo)

A weekly shopping trip became an hour-long aimless wander with an empty trolley when the customer realised they had won $3.8 million.

The Christchurch resident, who wished to remain anonymous, said he had no idea a Lotto ticket tucked in his wallet was a winner until he headed to Pak 'n Save Wainoni on Sunday to pick up some groceries.

It was the same supermarket where he had purchased the winning ticket.

"As we were heading to the supermarket my partner mentioned that someone had won big," he said.

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"I just replied, 'lucky bastard' and didn't think much more of it."

The man checked his ticket when he entered the store, as he usually did, and was instructed to head to the counter.

"I thought I'd won a couple of thousand. I was pretty stoked."

It was not until the employee handed his ticket back, along with a few moments to process, that he realised what he had won.

"I looked at the figure and thought they'd printed too many zeros in the cents section.

"I couldn't work it out, so handed it to my partner and said 'that's $3833 with a bunch of cents, right?' . . . We both looked at the Lotto lady and said 'are we reading this right?' and she smiled and said 'you definitely are – you better come with me'."

The new winners decided they would continue their usual shop, but the shock had set in.

"We wandered around the supermarket then got to the end and realised that we'd been pushing an empty trolley around for an hour.

"My mind was just gone – I couldn't think of a single thing."

The couple "called it quits" and went home to settle their nerves with a cup of tea before deciding they wanted to do some good with the prize.

"The first thing I want to do is help people – it's a great feeling knowing that I'll be able to help my family out.

"Otherwise I'm just going to take my time and make the winnings last."

Two winners shared Saturday's $7m Powerball jackpot, with the other residing in Auckland.

Both took home $3.8m. The other winning ticket was sold at Avondale Foodmarket in Auckland.