Mongrel Mob members make up almost half the patched gangsters in the Wellington police district, but it's the more organised violent gangs who give police the biggest headaches.

There are more than 400 patched gang members in the Wellington district, according to police data, almost half of whom are Mongrel Mob.

Police at the national headquarters said last week that they had little idea how many gang members were active throughout the country, but local police dispute that.

Detective Inspector Geoff Scott said, in a written response to an Official Information Act request, that defining gang numbers was "problematic" and recent attempts to quantify the membership of gangs had "proved to be inaccurate and basically unachievable".

But Detective Senior Sergeant Tim Leitch said district police had a pretty good handle on gang numbers in and around Wellington.

"There are 341 known patched members [of the bigger gangs], and if you include the additional patched members of the smaller gangs, we've got 418. We've got a relatively good idea of what we've got in the district.

"The numbers ebb and flow depending on whether people go to jail, move into other gangs or out of the region, or leave the gangs. [But we know] we've got 11 main gangs or groups in the district."

The Mongrel Mob were the largest gang, with 194 known patched members, principally in Porirua and the Hutt Valley, he said. They had almost four times as many members as the next largest, Wellington's Black Power, with 52 known patched members.

The Nomads had 34, mostly in Wairarapa, and there were 18 Full Blooded Islanders in Wellington.

Across the district there were also patched members of the Bandidos, Head Hunters, Hell's Angels, Highway 61, King Cobras, Rebels, Satan's Slaves and Tribesmen, Mr Leitch said.

But while the Mongrel Mob dominated the numbers stakes, their offending was often milder than that of other gangs, Hutt Valley area commander Inspector Mike Hill said.

"If you just added up total offences, of course the Mongrel Mob would be a higher number of crimes in total. But if we're looking at violent and serious offending . . . our concern continues to be the Head Hunters.

"They are committing offences that are staying under the radar of the public - high-level violence within the criminal networks."

Kapiti-Mana area commander Detective Inspector Paul Basham said that while the Mongrel Mob were prominent in Cannons Creek, police tried to engage with the gang. "We do keep an eye on the Mongrel Mob and their various criminal activities. But we are always looking for opportunities to work with them constructively when they or their affiliate groups want to engage positively . . . particularly around family violence and alcohol issues."

Despite official comment from police headquarters that gang numbers were unknown, Mr Leitch said district officers kept a close eye on things.

"We're monitoring what they're doing, who they're associating with and what offending they're doing. And we're taking opportunities to disrupt what activities we can."