A 10.7 kg gold nugget, about the size of a loaf of bread, has been discovered inside a box used by NSW Treasury officials as a wicket for their indoor cricket games.

Known as the Maitland Bar gold nugget, it was discovered in 1887 and purchased by the NSW Department of Mines that same year.

"Someone studiously decided they'd place it in a box," NSW Premier Mike Baird said today.

"The problem was they forgot to tell anyone and that box became used for hallway cricket."

The nugget is believed to be one of the purest ever unearthed and has been conserved ever since, as a link to the 19th century gold rushes.

When the State Government were trying to figure out what to do with the $3.7 million gold nugget, it was entrusted to Treasury - which is when it's more humble fate came to fruition.

Mr Baird said he has since instructed Treasury to "open every box they can find".

"My good friends in Treasury - I love them dearly, but that was not their finest moment," he added.