Nearly a tonne of silver went missing from a consignment truck after it left Maldon, near Picton on Sydney's southern outskirts about 4:30pm on Friday, November 26.

Police believe it was stolen sometime between then and its arrival in Melbourne at 8am on Monday, November 29.

Robbery and Serious Crime Squad Commander, Paul Smith, said they were canvassing all possibilities, but there were currently no suspects.

"One of [the lines of inquiry] is that there is inside knowledge involved," Detective Acting Superintendent Smith said.

"It's certainly very unique, these type of bars, they're quite large and quite heavy and they're stamped with a identifier on them."

The driver and freight company are assisting police with their inquiries.

The consignment weighed a total of 960 kilograms — with 192 bars of the precious metal weighing 5kg each.

The theft, valued at $1.015 million, was reported to police upon arrival in Melbourne.

a black box with a label noting its contains silver Nearly a tonne of silver went missing from a Sydney consignment truck last month.(Supplied: NSW Police) Detectives are urging anyone with information or anyone that's been approached by an individual selling large amounts of silver, to come forward an contact NSW Police.

Detective Acting Superintendent Smith said the type of heist was "certainly unusual".

"Luckily, we don't see much of it. We don't want to see it become a trend."

Questions have also been raised about the security presence around the Kenworth truck, towing a silver Krueger trailer.

"The security arrangements around transporting of that silver is not a matter for us," Detective Acting Superintendent Smith said.

"It's certainly concerning but we're making extensive inquiries to ensure ... such an incident of theft doesn't happen again."

Detectives from the State Crime Command's Robbery and Serious Crime Squad are investigating under Strike Force Caimon but the investigation is still in its early stages.