Two vessels with specialist oil recovery equipment and personnel Sunday began cleaning up oil spilled from a Liberian-flagged cargo ship grounded on a reef off New Zealand's North Island as severe weather was forecast to hit the area.

Maritime New Zealand (MNZ), the country's shipping authority, said Sunday that two of the four New Zealand navy vessels in the area were also testing oil recovery equipment for use around the Astrolabe Reef, about 12 nautical miles offshore, near Tauranga, where the 47,000-tonne Rena, has been grounded since early Wednesday.

Preparations are also underway to transfer heavy fuel oil from the ship to the Awanuia, a double-hulled bunker barge, capable of holding 3,000 tonnes of oil.

MNZ national on-scene commander Rob Service said it would take a matter of hours to prepare for the direct transfer of oil, but several factors would determine exactly when that process would begin, under the direction of salvage firm Svitzer Salvage.

No further oil had been seen leaking from the vessel since Saturday and the oil spilled then had been dispersed, said Service.

"The removal of fuel from the ship remains the top priority. Pollutants on board the vessel including paint, grease, hydraulic oils and lubricants are being hand carried off the vessel on to a small support vessel," said Service.

"These are maintenance goods that are carried on most vessels. This is a labor-intensive but necessary contingency task."

Two ocean-going barges -- the Northern Quest and the Phoenix -- were tasked with recovering heavy fuel oil in the water and 10 specialist personnel from Australia were assisting.