Another two protesters have been arrested outside the New Zealand Defence Industry Association conference in Palmerston North.

The two men were arrested for disorderly behaviour after climbing on top of buses as part of a protest.

Police said the men were "arrested without incident, complied with police instructions and came down from the roofs willingly".

The two were released and given pre-charge warnings, police said.

Ten protesters were arrested yesterday, on the first day of the conference, for assaulting police, disorder and obstruction.

One woman was detained by police after lying down beside a bus and refusing to move.

Yesterday's march from the Square was peaceful, but some protesters outside the venue "acted in a way that created safety issues, disrupted traffic, inconvenienced the wider public and in one instance an officer was spat at," Inspector Peter Thurston said.

Protest organiser Valerie Morse said yesterday the intention was to blockade and delay delegates attending the event.

"The peace movement is using tactics of non-violent direct action to stop war at its source: with the people who directly profit from waging war."

"We expect that the police and security will respect the human rights of people who are standing against war."

"Actions will continue over the next two days."