Shipping officials are investigating why a petroleum drilling ship broke from its moorings during a storm off the Taranaki coast.
Heavy seas 40km offshore snapped anchor chains on the Noble Discoverer on 27 April, forcing it to run for deeper water.
Some of the 114 crew were reported as saying the ship drifted close to a Maui gas platform and to the large tanker that collects oil from the Tui field.
Shell Todd Oil Services says the Noble Discoverer disconnected from the wellhead before the storm, closed the well and passed almost 3km from Maui and 10km from Tui.
Maritime New Zealand says officials need to find out what happened.