Crews wrapping up the removal of the Robert E Lee statue in Richmond in the state made the discovery on Monday, with the likely contents said to be long sought-after.

Lee has been a deeply divisive figure in the US, with various places removing references to him from their public spaces in the light of last year's Black Lives Matter movement.

Richmond's statue was removed in September, with crews staying behind dismantle the plinth and search for the buried artefact.

News reports from 1887 say that the box being searched for was placed at the site in a cornerstone laying ceremony, which was attended by thousands of people.

The box in question, which is expected to be opened on Tuesday, is thought to contain, among other things, a rare photograph of assassinated US president Abraham Lincoln.

Virginia Governor Ralph Northam tweeted an X-ray of the box and said there may be "coins, books, buttons, and even ammunition from the Civil War".

It was found surrounded by granite and other construction material at ground level, workers say, and sitting in water.

Once the copper box was carefully removed, it was wrapped in bubble wrap and taken away from the site to be examined.

A similar box was found earlier in the month, but once pried open was found only to contain a few books and coins, leading investigators to theorise it was left by construction staff and was not the trove of artefacts they were hunting for.

The Confederate monument had stood among four other massive statues on Richmond's Memorial Avenue, but the city removed the others last year.

The area surrounding the monument became a hub for protests against racism, seeing the occasional clash between police and demonstrators.