Hundreds of delegates at a defence industry conference couldn't get in after protests at the Auckland venue by peace groups.

The chairman of the New Zealand Defence Industry Association, Bernie Diver, said he was annoyed up to 350 of those who had paid to go the conference were prevented from getting in.

Police advised them not to try after skirmishes between protesters and security guards and a confrontation between protesters and two delegates who tried to get into the Viaduct Events Centre in Auckland.

Diver said he was disappointed the police didn't clear a way for the delegates to get in and the outcome was a bad look for Auckland and New Zealand.

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One of the two delegates who tried to get in to the venue, and identified himself as Ernie, a communications company representative from New York, said he was disappointed to be prevented from getting into the building.

There were about 150 protesters.

Ernie said there should have been more police there and police on horses would have been more effective.

The association says it is a "misunderstood" sector that generates $60 million for the economy by providing support services to the NZ Defence Force. Its conference in Wellington last year was also disrupted.

Diver said companies which work in defence supply had been unfairly targeted.

''It's simply unjustified and unfair to the many people and suppliers who are doing an honest day's work by supplying our New Zealand forces as they undertake missions such as rescuing ships in the Southern Ocean, providing disaster relief in the Pacific Islands or enabling Antarctic science.''

Te Ao Pritchard, a spokeswoman for peace group the Pacific Panthers, said the conference allowed manufacturers of weapons to trade with each other.

''In this country we're opposing profiting from war. This expo is a disguise that the military is using to say the purpose is to protect Aotearoa but it's really about the manufacturers," she said.

"We don't want anyone to get in there to start trading or making money off our lives."

Diver said the conference went on as planned and included a speech by Defence Minister Gerry Brownlee which outlined details of the Defence Capability Plan 2016.

Protestors at the Defence Industry Association Conference. Photo / Grant Bradley
Protestors at the Defence Industry Association Conference. Photo / Grant Bradley

The plan outlines a $20 billion programme of capital investment, over a 15-year period, including $1.7b to modernise the Defence estate, while retaining a presence in all current camps and bases.

Diver said organisers would review security arrangements for the conference which continues tomorrow.