The parents of three-year-old Pipi Quinlan got a nasty shock when they found she had bought a $20,000 earth-moving digger on auction website Trade Me.

Pipi, who decided to play on the computer while the rest of her family were asleep, entered the Trade Me site that her mother was already logged on to, the Rodney Times reported.

With a few clicks of the mouse, she won the most recent auction listed on the site's homepage - a Kobelco digger for $20,000.

"The first I knew about it was when I came down and opened up the computer," Pipi's mother Sarah told the newspaper.

"I saw an email from Trade Me saying I had won an auction and another email from the seller saying something like 'I think you'll love this digger'."

Ms Quinlan said she had auctions on several toy sets and assumed she had won a toy digger set.

"It wasn't until I went back and re-read the emails that I saw $20,000, and got the shock of my life."

Ms Quinlan immediately called Trade Me and the seller to report what had happened.

Trade Me reimbursed the seller's costs for the auction and the digger had been relisted.