The Liberian-flagged Rena has been stuck for 12 days on a reef 14 miles (22 km) off Tauranga on the east coast of New Zealand's North Island, having already spilled about 350 tonnes of toxic fuel and some of its hundreds of containers into the sea.
Salvage teams were adding extra pumps to speed up the recovery of the oil, as thick as peanut butter, from the 236-metre (775 feet) vessel through holes in the side to a barge.
More than 70 tons have been recovered, but fears are that bad weather will halt the operation and possibly send the stern section, which contains more than 1,000 tons of oil, tumbling into 60 metres of water.
"If the vessel falls off the reef it could puncture a tank. You don't know what's going to happen if it falls off the reef," said Bruce Anderson, spokesman of Maritime NZ which is responsible for supervision of the shipping industry.
The agency said a crew of three salvage team members would remain on board overnight to continue with pumping efforts.
Conditions around the ship have been good but forecasts are for winds to rise to 60 kph (40 mph) and sea swells of 4 metres.
The salvage company said the ship is precarious and further spills of oil not in tanks seems inevitable.
"That ship is very, very sick. She is fractured, she is broken, she is on her knees...There probably will be more oil leaving that vessel if the weather turns nasty," Matt Watson of the Svitzer salvage told Radio New Zealand.
He said if the stern section of the ship sinks, it would complicate the recovery and require divers.
Still, Svitzer Salvage team leader Captain Drew Shannon said the ship had its own unique challenges.
"Our team is taking their time to remove the oil safely to minimise further risk to the environment," he said.
"We are also working feverishly in the background with planning and logistics on the removal of containers. Our priority however remains the removal of the oil from Rena."
Separately, the company that chartered the 47,320 ton ship met the government and gave a commitment to contribute to the clean-up costs, although it disputed it had any liability.
Liabilities
MSC has said the liability for the grounding and salvage is the ship's owners, Greece-based Costamare Shipping Inc., who last week apologized in a video statement.
The ship's captain and second officer, both from the Philippines, are due to reappear in court on charges of operating the 47,320 ton ship in a dangerous manner.
Beaches, fouled with dinner-tray sized lumps of oil, have been largely cleaned up after thousands of volunteers joined soldiers and specialists.
"It feels good now, but we don't know how long it will last, the threat of pollution will be hanging over us for ages," said local resident Kim Greene.
Oil has washed up along about 60 kms (37 miles) of the coast, which is popular with surfers and fishermen. Nearly 1,300 birds have died in the spill, which is seen as New Zealand's worst environmental disaster in decades. (Reuters)
