Six metre swells overnight caused the stern and forward section of the stricken cargo ship Rena to move, spilling containers into the rough seas and creating a moving debris field.

Maritime New Zealand (MNZ) said observation flights showed containers and debris had fallen from the ship as it was hammered by massive swells last night.

Response and recovery manager David Billington said two containers had been spotted floating about two kilometres from the wreck.

Bags of milk powder and timber were also floating in a debris field spreading about two nautical miles south east of the vessel, he said.


He advised boaties to avoid the area between the Rena and Motiti Island.

"There is timber in the water, which could certainly cause damage if vessels came into contact with it at speed."

Mr Billington said the storm had also damaged bulkheads at the front of the stern section and caused structural damage to the forward section of the Rena.

Two tug boats, a fast response vessel, one barge, and a plane were assessing whether sea conditions would allow debris collection to get under way, he said.

National on-scene commander Rob Service the storm had spread a small amount of oil about one nautical mile to the east of the Rena.

Observers have also noted some dark patches of oil around the wrecked ship.

Mr Service there was the potential for some oil to come ashore in the coming days.

Bay of Plenty Regional Council's harbourmaster has issued a navigational safety warning over the latest debris spill.


The debris was moving between the Rena and Motiti Island, though changing tides and weather conditions could alter its course, a statement said.