PORTLAND – Portland police have doubled patrols and confiscated guns as they seek to defuse what officers say could become a violent struggle for territory between rival motorcycle gangs.

Dozens of members of groups like the Hells Angels and other clubs aligned with them have been arriving from other parts of Maine and New England and staking their claims in the state’s largest city.

The trouble dates back several weeks to the formation of a Portland chapter of the Black Pistons, a motorcycle club affiliated with the Outlaws, a national gang and rival of Hells Angels, police say.

The presence of so many motorcyclists wearing their club patches is intimidating to Old Port patrons, according to police.

“We cannot allow both groups to come together for an aggressive interaction,” Portland Police Chief Michael Chitwood said. “I can’t have shots being fired or chains being pulled or people being beaten with ball-peen hammers in the middle of the Old Port some Friday or Saturday night.”

The Portland conflict comes at a time of heightened violence between rival motorcycle gangs including beatings, stabbings and killings in recent weeks as far away as Las Vegas and as close as Laconia, N.H.

Over the weekend, two prospective members of the Hells Angels were shot and wounded in central New Hampshire. Earlier this year, people have been killed in Nevada and New York in violence between motorcycle gangs.

So far Portland police have reported no serious incidents involving bikers, though two guns were seized and two arrests made Friday.

Massachusetts-based members of the Outlaws have been recruiting for the new Black Pistons club, even approaching members of the former FSU posse.

Clubs that have been established in Maine for years, including the Iron Horsemen, Mountain Men, Vietnam Vets, Saracens, Exiles and Hells Angels responded by coming to Portland and positioning themselves in front of bars where FSU members are known to congregate.

Neither side wants to back down for fear of appearing weak, and it’s the contest of wills that has authorities concerned.

“If these guys start a war, somebody is going to get hurt,” Chitwood said. So police are trying to make Portland an inhospitable place for a conflict.

Last weekend, Lt. Judith Ridge and Sgt. James Sweatt videotaped members of the groups and recorded vehicle registration numbers. Police also have doubled their presence in the Old Port district.

Police also requested the owners of at least three Commercial Street bars to close early Friday to forestall any trouble.

“We just hope they kind of resolve their differences before somebody gets hurt,” Chitwood said.