A 10.7-kilogram gold nugget, known as the Maitland Bar gold nugget, has been loaned to the Australian Museum for display.

The nugget was discovered in 1887 at Maitland Bar on Meroo Creek and is said to be one of the purest ever unearthed.

It was last valued at $3.7 million, but New South Wales Premier Mike Baird has revealed that its circumstances in recent years had been much more humble.

Years ago the State Government was trying to work out where to put the nugget for safekeeping after it was entrusted to Treasury.

"Someone studiously decided they'd place it in a box," Mr Baird said.

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

Public servants continued to use the box as a wicket for impromptu cricket games not realising what it contained, until one day someone decided to open up the box and found the massive gold nugget.

Maitland Bar gold nugget: Discovered in 1887 in the Hargraves district

Discovered in 1887 in the Hargraves district Tenth-largest gold nugget ever found in NSW

Tenth-largest gold nugget ever found in NSW Has gold content of 8.87kg

Has gold content of 8.87kg The nugget was displayed at local banks in the 1930s

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

The NSW Premier described the nugget, which is about the size of a loaf of bread and has a gold content of nine kilograms, as magnificent.

"I have, for the record, asked Treasury to open every box they can find," he added.

The nugget was bought by the NSW Department of Mines in 1887, the year of Queen Victoria's Golden Jubilee.

It has since been conserved by the State Government as a link to the gold rushes in the 19th century.

"We all know about budget problems, don't we? There's all types of budget problems," Mr Baird said.

"Treasury kept this little secret from me."

The nugget will be on display for four days in the Australian Musuem's historic Long Gallery, along with the country's first bank note, which is on loan to the museum by Westpac.

Westpac, the NSW Government and the Australian Museum also announced a $9 million restoration program for the Museum's Long Gallery.