One million dollars’ worth of silver bullion has mysteriously disappeared somewhere on the road between Sydney and Melbourne and police are investigating if somebody with inside knowledge is behind the brazen heist.

NSW Police say 192 individual five kilogram silver bars were pinched from a truck which left NSW on a Friday afternoon last month and arrived in Melbourne at 8am the following Monday.

The consignment was being transported by a Kenworth truck and silver Krueger trailer.

It’s an unusual kind of theft, Detective Acting Superintendent Paul Smith, who’s the Robbery and Serious Crime Squad Commander, told reporters on Tuesday.

“Luckily we don’t see much of it,” he said.

“Certainly we don’t want to see it become a trend, hence why we’re deploying a lot of resources and time to catch those involved.”

Police want anyone who’s been approached by someone trying to sell large amounts of silver to come forward.

They have released photos of the silver bars, which have a distinctive stamp.

The silver bullion is estimated to be worth $1,015,000.

There are no suspects but police have several lines of inquiry, including whether people who had inside knowledge about the consignment might have been involved.

The Kenworth truck is owned by a large freight company based in Sydney.

The security arrangements around the transportation of the silver are not a matter for police, Mr Smith said, but the driver is helping with the inquiry.