Police in areas of Rochdale, Bury, North Manchester, Oldham, Bolton and Salford have been undertaking raids on homes and scrapyards.
The searches were in aid of finding scrap metal that had been stolen from various other areas locally.
Supt Craig Thompson said: “Since Operation Alloy was launched more than two years ago, we have made huge inroads into tackling metal theft.
“However, despite a sharp drop in incidents of metal theft, we know there is still a culture that exists among thieves who believe they can off-load stolen metal onto scrapyards.
“Any scrapyard dealer who knowingly accepts stolen goods or pays cash for metal is propagating this cycle of criminality, creating a market for thieves for prosper, and that is exactly why we have taken this action today. If a burglar knows he can sell stolen metal to a rogue dealer, it will entice them into committing offences that can cause real hardship to businesses and victims.
“For example, if a pensioner has her boiler stolen in winter they will be unable to heat their home which could put their life in danger. We also know of businesses that have been forced to shell out hundreds of thousands of pounds to pay for repairs as a direct result of metal thieves.”
“What today is all about is targeting those rogue dealers who are suspected of lining their own pockets and making huge swathes of cash by knowingly selling stolen metal,” added Supt Thompson.
“In terms of officer numbers and the sheer scale of the investigation, this is the biggest operation ourselves and British Transport Police have run which shows our determination to tackling metal theft.”