The police operation in Bethlehem has traffic backed up for kilometres.

About a hundred bike gang members are the objects of a massive police operation under way in Bethlehem, near Tauranga.

The massive operation has backed up traffic on State Highway 2 for kilometres. Hundreds of cars are stuck. Traffic coming into Tauranga was said to be blocked back to Omokoroa after police closed a roundabout and a lane of the highway.

Reports say more than 40 motorcyclists have been stopped.

Rosalie Crawford / SUNLIVE A Bethlehem resident says the police are only breath-testing gang members - cars are not being stopped.

Police are remaining tight-lipped about what is happening, other than to say it is focused on "road policing".

However, it is understood more than 100 gang members from Head Hunters, Greazy Dogs and Mongrel Mob are in the area for the unveiling of a memorial at Wairoa Marae to Tane, who died a year ago. Apparently police have taken advantage and brought in two booze buses and enough officers to man them and set up a massive breath-testing operation.

SunLive is reporting that residents have spotted at least 40 police officers and 20 police cars at the roundabout near the birthing centre in Bethlehem.

Rosalie Crawford / SUNLIVE There are at least 40 police officers and a couple booze buses in the small Bay of Plenty town for the operation.

One caller said the road between the roundabout and the Wairoa Bridge was heavily congested with large numbers of policemen posted at either end.

"We can't get into the back of the supermarket," one said.

Some roads in the area are closed.

Rosalie Crawford / SUNLIVE A Bethlehem resident submitted this photo of activity at the roundabout to SunLive.

A Facebook post said, "[the police at Bethlehem] haven't done any stopping of vehicles - only stopping patched gang members due to Tane unveiling".

In a press statement released about 3.30pm from Bay of Plenty police, officer in charge Senior Sergeant Denis Murphy said police were monitoring outlaw motorcycle gang members "movements with a particular focus on road safety and on ensuring our communities are not harmed or intimidated."

Police understood the gang members were in the area to attend a memorial service.

Historically, gang rides have caused public concern with members riding en masse, the statement said, adding that "rides like this intimidate other motorists and are a deliberate and provocative breach of traffic laws".

"They are also inclined to endanger members of the public, ignoring road safety rules, with complaints of dangerous driving, driving with the wrong class of licence and driving under the influence of alcohol and drugs.:

Police acknowledged the delays to motorists were unfortunate, but made no apology for policing gangs.

Police would like to thank the public for their understanding and support.