Drums containing a chemical which forced the evacuation of Port Taranaki have been identified, but fire crews must now decide how to get them off the ship.
Firefighters were called to the port after smoke was seen coming from the cargo ship the Poavosa Wisdom just after 1pm.
The port was evacuated and crew were ordered off several vessels while firefighters worked to find the source of the smoke.
The port's chief executive, Roy Weaver, says the toxic gases have been traced to a 209-litre drum and a 20-litre drum of aluminium phosphide used to fumigate bugs in imported feed.
Firefighters are working to get the drums off the ship, but Mr Weaver says that can be difficult because the holds of ships are tight spaces. They will seal the drums, then remove them from the ship and dispose of them.
Mr Weaver says it appears no one inhaled the toxic gas.
The Port of Taranaki and Maritime New Zealand are investigating.