The majority of the chapter "patched over" after being deported from Australia, Williams said.
More than 110 police staff, including from the National Organised Crime Group (NOCG), executed search warrants at 10 properties in the raids.
Molotov cocktails allegedly found during the raid.
Ten people were arrested and face charges, including participating in an organised crime group, money laundering, conspiracy to deal methamphetamine, supplying methamphetamine, supplying cocaine, unlawful possession of firearms, and unlawful possession of explosives, police said in a statement.
Nineteen vehicles were seized - five motorcycles, one light truck, one heavy truck, seven cars, four utes, and a quad bike.
Other items seized included ammunition, and various amounts of cannabis, methamphetamine, and cash.
Williams said in the statement the Mongols were a well-established criminal group known for drug trafficking, firearms and violent offences.
"The majority of this Bay of Plenty gang were deported from Australia and were from one of the Banditos chapters in Brisbane," he said.
"During the course of this lengthy investigation, NOCG has been able to support a Bay of Plenty response to combat and prevent violent incidents stemming from this organised crime group, which have been well documented through the media."
These have been as recent as June 12 and again on June 15, where senior members are now before the court on serious charges, and a number of firearms and explosive devices have been seized, Williams said.
This proactive action was taken to prevent an attack on a rival gang, he said.
"What this investigation will allege is that this organised crime group was involved in the sale and supply of methamphetamine and cocaine on a commercial level into the Bay of Plenty as well as across the North Island, causing significant harm to our communities," Williams said.
"The ongoing violence between this organised crime group and other local gangs is simply about controlling a share of this drug market, and all these gangs have made it clear that they are prepared to use violence to protect their share.
"This includes not only arming up, but a very clear propensity to use these firearms and commit other violent acts such as arson, serious assaults, aggravated robberies and serious violence, seriously impacting on the wellbeing of Bay of Plenty communities at large."
In total there have been six known shooting incidents involving the Mongols and other gangs, police said.
Detectives from the National Organised Crime Group have this morning executed search warrants targeting the homes and associates of the notorious Mongols motorcycle gang. Photo / Mike Scott
Some charges have been laid in relation to these and inquiries continue, they said.
While Operation Silk took place in the Bay of Plenty, Auckland NOCG also ran Operation Nestegg, which focused on Auckland-based Mongols.
In May this year a number of search warrants were executed in Auckland and Tokoroa that were linked to this investigation.
Items seized included five firearms, approximately $400,000 cash and half a kilogram of methamphetamine.
The combined investigations will have a serious impact on the influence and offending of this gang for some time to come.
Police also continue to ask the public for information on another senior Mongols member Brodie Collins-Haskins, of Auckland, who is facing several charges.
"Our view would be if you see him or observe him please contact your local police."
Collins-Haskins should not be approached, he said.
The search warrants used today in Papamoa and Te Puke were the culmination of an investigation led by the Tauranga-based squad of the National Organised Crime Group.
Detectives from the National Organised Crime Group have this morning executed search warrants targeting the homes and associates of the notorious Mongols motorcycle gang. Photo / Mike Scott
The NOCG group was set up in the Bay of Plenty two years ago to specifically target the threat of motorcycle gangs, in particular the arrival of Australian groups, and smuggling channels through the port.
