"[The protesters] were pushing the police to get into the area; there was lots of pushing."
James said the protesters were sitting in front of the police and chanting. She was not sure if people had been hurt but she saw someone holding their face.
Police can be seen shoving protesters backwards.
A police spokesperson says the actions of police are dictated by the situation presented to them.
Protest organisers Auckland Peace Action organised the blockade to stop the opening of the forum at 8am. More than 500 people have said they will join the protest.
Auckland Peace Action spokesperson Virginia Lambert said the conference was about how companies can make more money from "wars, disasters and human misery".
"The arms trade simply has no place in a civilised society.
"We are taking non-violent direct action to stop this expo from happening."
The world's largest nuclear arms manufacturer, Lockheed Martin, is the main sponsor of the forum, which will be attended by arms dealers from all over the world.
Protesters will be addressed by former Auckland mayoral candidate Chloe Swarbrick, Nobel Peace Prize nominee Dr Helen Caldicott, Auckland councillor Cathy Casey and Patrick Hinchcliff, the grandson of the AUT University founder.
READ MORE:
Protesters forming human blockade
The blockade is part of the Week of Peace, a series of peace actions to counter the forum and presence of navy warships in Auckland for the 75th Anniversary celebrations of the Royal New Zealand Navy on the Waitemata Harbour.
"We want to work for peace, not prepare and fund wars," Lambert said.
The anniversary celebrations were brought forward a day because of expected bad weather.
The New Zealand Defence Industry Association earlier said it is a "misunderstood" sector that generates $60 million for the economy.
NZDIA chair Bernie Diver said the forum will bring together 170 businesses from a sector that employs 2500 people and pays $125 million in wages.
Some suppliers provided weaponry, but he said the vast majority supplied New Zealand soldiers with equipment to undertake maintenance, repairs, logistics, engineering and other civil services.
"Close to 1000 people are employed nationally in food and services alone, and a further 600 in repair and maintenance contracts," he said.
At last year's forum in Wellington around 75 protesters, one dressed as the grim reaper, chanted "blood on your hands" attempted to stop delegates. Police arrested more than two dozen after scuffles turned violent.
This year Auckland Peace Action, which calls the defence industry "death merchants", has listed plans for non-violent protests on its Facebook page.
Diver said the "death merchants" label was "misguided".
Although most of the defence force's work was civil, such as emergency relief services after Monday's Kaikoura earthquake, Diver said "when they are in harm's way we want [New Zealand soldiers] to be the best equipped they can".
The two-day event at Auckland's Viaduct Events Centre is also likely to draw more foreign dignitaries as it coincides with the Royal New Zealand Navy's 75th anniversary celebrations.
- with AAP