Williams has confirmed one of the firearms seized yesterday was an MP38 submachine gun.
The three people arrested today will appear in the Tauranga District Court and face charges including participating in an organised crime group, unlawful possession of firearms and conspiracy to deal methamphetamine.
Williams said police anticipate there will be further arrests made in relation to Operation Silk.
He has previously said 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.
The lengthy investigation that had targeted the gang had combated and prevented violent incidents, he said.
Police continue to appeal for information about the whereabouts of senior Mongols member Brodie Collins-Haskins of Auckland, who is facing several charges.
Detective Superintendent Greg Williams of the National Organised Crime Group during yesterday's press briefing. Photo / Brett Phibbs
Yesterday, Williams said Collins-Haskins "could be anywhere".
The Australian national, 26, should not be approached by members of the public.
"Our view would be if you see him or observe him please contact your local police," Williams said.
Detectives from the National Organised Crime Group executing search warrants yesterday. Photo / Mike Scott
