Police have labelled the actions of around 20 Greenpeace protesters who barricaded Fonterra's Auckland head office this morning as "irresponsible" and a waste of police resources.

Around 850 people were evacuated from the Princes St building after an identified box was left unattended chained to a handrail in an elevator.

Police treated the box as a potential threat and specialist services were called in to determine the contents of the box.

An hour later police determined the box was non-threatening, containing only a speaker system, and staff were able to return to the offices.

Acting Auckland City Area manager Inspector Mike McIlraith said charges were likely to be laid and investigations were continuing.

"Police who attended the incident today are concerned that the behaviour of the protesters was irresponsible and unnecessarily consumed a lot of emergency services resources."

Greenpeace were protesting Fonterra's use of palm kernel as stock feed, which is linked by the organisation to deforestation in South-East Asia.

Demonstrators this morning erected a 1.8m by 2.4m long barricade fixed with television screens inside the foyer of the Princes St offices.

Greenpeace spokesperson Simon Boxer said the protest had only barricaded one entrance and staff were able to pass through five other entrances to the building unhindered.

"10 people peacefully handed out leaflets explaining what we were doing," he said.

Mr Boxer said the television screens were broadcasting footage from a Greenpeace trip last week to Indonesia, looking at the deforestation of native forests.

Greenpeace claim Fonterra import one quarter of the world's palm kernel, and native forest in Indonesia is being cleared at a rate of two per cent per year in order for the crop to be grown.

"We hope the message has gone in there and Fonterra take corporate responsibility for the deforestation that is happening in Indonesia at this very minute."

A Fonterra spokesperson said the company did not want to comment on the protest or the company's use of palm kernels.