A "suspicious" device was found at an address in McCarty Avenue, Epping, about 22km north of Melbourne's CBD, where one of the four men was arrested.
The bikies were expected to be taken to the crime squad headquarters in St Kilda Rd, in central Melbourne.
The 10 properties hit with search warrants were premises connected to members and associates of the Hell’s Angels Motorcycle Club.
A stolen jet-ski, hydroponic equipment, guns, vehicle’s and an earth-mover were seized by police.
The arrests are the result of operation Resound which police revealed yesterday in the wake of concerns about a full-scale war looming between the Hells Angels and the Bandidos.
Top cops announced a "sustained" operation in Victoria, codenamed Resound, in response. It will be led by the anti-bikie Echo Taskforce.
Deputy Commissioner Graham Ashton said the operation would continue until the threat of violence between the two deadly gangs "calmed down".
Police had "credible information" of a looming war, he said, warning members of both clubs that violence would not be tolerated.
The tension between the two gangs ratcheted up as a result of Hells Angels invading a Bandido-aligned gang's clubhouse just before last Friday's ambush of Bandidos sergeant-at-arms Toby Mitchell, which saw him shot in the arm.
The Angels are suspected of smashing security cameras during a "run-through" of the Melton clubhouse of the small outlaw gang the Diablos, before its members called on their Bandido mates for help.
Bandido strongman Mitchell, arriving at the scene, was hit for the second time in 16 months.
The Herald Sun has been told CCTV that could have captured the violence was smashed as Hells Angels members tore through the Norton Ave clubhouse.
Those cameras were covering an area around the clubhouse but were useless by the time the shooting occurred, about 10pm.
As Bandidos pulled up on Friday night, dozens of shots were fired by men who had pulled up in as many as 10 vehicles.
Police declined to discuss possible motives for the shooting, but have confirmed talks with both clubs have achieved little.
It is suspected the Hells Angles' Thomastown Nomads chapter, considered enforcers, were responsible for the carnage, ramming a car containing Mitchell.
Police have held talks with both clubs, with members of the Hells Angels in particular giving no assurance of a truce.
An email circulated by force command warned the Bandidos were in conflict with the Angels, with threats of "escalating violence" over the Melton incident.
Among the Bandidos who had arrived at the Diablos when the shooting began was heavyweight boxer Nick Zakharia.
Zakharia, a Mr Australia body-building championship winner, was jailed in the 1990s for posting cocaine from the US.
He is an extremely well-connected figure in the Melbourne underworld and, with Mitchell, a member of the Bandidos' Brunswick chapter.
Mitchell was shot in a near-fatal ambush in November 2011 outside their clubhouse.
A prominent Bandido has declined to comment on the situation. Bandidos were seen in the afternoon in Clarendon St, South Melbourne, in supporter gear.
"There are probably two clear messages here from us today, and that is if you are a member of an outlaw motorcycle gang or affiliated with one of these gangs and you are planning any escalation in violence, our message to you is quite clear that that will not be tolerated," Mr Ashton said.
He said the community should be reassured police would act "quickly and decisively".
"Our message to you is that will not be tolerated. We have a plan," he said.
Assistant Commissioner Stephen Fontana said the force had thrown its resources to target the gangs until the threat was over, including heavily armed critical incident response team, public order response, regional and road police.
Police officers have been warned to be aware gang members will be armed.
Mr Fontana said the "threat was real".
"I think when you've got very public shootings like we had last Friday night with over 30 shots and other activity, the threat is real," he said.
"The thing that concerns us is that it plays out in the public arena. Of course, we're out there every day pulling over motorists, checking people and we're sending out that caution.
"We have concerns about a few, it is escalating and we're warning our members to take care.
We don't want anyone getting hurt." An email sent to officers has warned them to take extra care when dealing with gang members.
The warning was issued after the shooting at Melton of top Bandido Toby Mitchell on the weekend.
Echo Taskforce talks with the leaders of the gangs has apparently failed, with fears national and even international members could influence the escalating feud.
"These people don't have any regard for the law ... we're going to try and stop that and we're asking them to just ease up," Mr Fontana said.
Mr Fontana said both groups had networks internationally and throughout Australia and could draw on them.
He also said gang members from Sydney who had based themselves in Melbourne, some of a Middle Eastern background, were having an influence.
The Hells Angels, who believe they are the strongest club in Melbourne, are outnumbered by most other major bikie gangs, including the Bandidos.