Police in Sydney have seized more than $6.5 million in cash and property they believe was stolen in the city's north and in Melbourne.

Detectives raided a storage unit in the inner-Sydney suburb of Waterloo just before 5:30pm (AEDT) on Wednesday.

They found $2 million in cash plus foreign currency and 120 kilograms of silver bullion.

Gold and silver jewellery, precious stones, antiques, heirlooms, fake identification and five guns were also discovered in the unit.

Police say they believe the items were stolen in a string on burglaries of homes on Sydney's north shore and during a break-in at a storage facility in the Melbourne suburb of Ivanhoe.

Acting Assistant NSW Police Commissioner Mal Lanyon says there have been scores of similar robberies in Victoria.

"There certainly is a level of sophistication," he said.

"We believe there may be a number of owners both of commercial and residential premises who are unaware that their safes have been tampered with and entered, and certainly unaware that their property may have been taken.

"We would ask people to actually have a look, ensure that there has been no break and enter at their premises or certainly within the safe.

"If they do locate one, report it to your local police so that we can follow it up."

He says police are in the process of tracking down as many owners as they possibly can.

"The 120 kilograms of silver bullion we believe may be as a result of melting down silver jewellery that has been stolen in some of these offences," he said.

"Hence the recovery of some of that property will be very difficult to get back to the owners but that is why we are appealing to members of the public who may have been subject to an offence to come forward."

Wednesday's search came after officers from Strike Force Better arrested two men, aged 33 and 56, at a Randwick boarding house on December 19.

The pair were then extradited to Victoria where they were wanted on outstanding warrants.

Police say inquiries in relation to offences committed in New South Wales are ongoing.