New Zealand's Prime Minister John Key has said serious questions needed to be answered about how a container ship could run aground and leak oil near one of the North Island's most environmentally sensitive areas.
Mr Key, who flew over the accident scene 22km off the coast of Tauranga, said two government probes had been launched into how the 'Rena' ran aground on the reef in calm conditions early last Wednesday.
The accident seemed inexplicable, Mr Key said.
"People know about the reef, and for it to plough into it for no particular reason - at night, in calm waters, tells you something terrible has gone wrong and we need to understand why," he told reporters.
A major salvage operation is under way to try and contain the 5km-long oil slick.
The 47,000-tonne container ship is stuck on a reef about 8km from the Bay of Plenty, which is one of the country's most spectacular coastlines.
Maritime New Zealand said an Auckland-based tanker normally used to refuel cruise liners had arrived, and salvage crews hoped to begin pumping the 1,700 tonnes of heavy fuel aboard the 'Rena' onto it later today.
The deployment of barges is the first time response teams have been able to get out on the water and attack the oil spill, which has already killed a number of seabirds.
Previously, they had been limited to spraying chemical dispersants from aircraft and helping affected wildlife as they waited for specialist equipment to arrive.
The New Zealand government has warned that the accident could become the country's worst maritime pollution disaster in decades if the 'Rena' sinks, spewing oil into the pristine bay, which is home to whales, dolphins, seals and penguins.
With weather conditions expected to deteriorate on Tuesday, the vessel's owners, Greece-based Costamare Inc, said removing the oil from the stricken vessel was the top priority.
"Minimising any impact to New Zealand's coastline is the absolute priority for Costamare Inc and the current primary focus of the salvage operations is the safe transfer of the vessel's fuel oil from her tanks," it said in a statement.
While the Liberian-flagged vessel was badly damaged when it hit the reef, Costamare said "evaluations so far indicate that hull stresses are within allowable limits and that there is no deterioration of the ship's condition".
Officials hope removing the oil will help efforts to refloat the ship.
However, they describe the salvage operation as complex because the vessel is in the unique situation of having one end stuck hard on the reef while the other end is still floating.
Toxic discharge has already killed a number of seabirds, with six Little Blue penguins and two shags receiving treatment at wildlife rescue centres after being found coated with oil, MNZ said.
Teams were scouring the Bay of Plenty's beaches and islands for any other affected wildlife but indications so far were that none of the oil slick had blown ashore, it added.
Some 200 people, including specialists from Australia, Britain, Holland and Singapore, have joined the oil slick response team, with 300 defence personnel on standby if needed for shoreline clean-up work.
New Zealand health authorities on Sunday warned people not to eat seafood from the bay until further notice.
"Any seafood that has off or petrol-like odours should be avoided," it said.
