Salvage crews pumped oil Monday from a stricken cargo ship teetering on a reef off the New Zealand coast, after the weather cleared enough to restart work on the precariously listing vessel.

More bad weather predicted for later Monday could hamper or even end the salvage attempts. The ship is listing at a steep angle and has major structural cracks. Experts say it could break apart or slip from the reef at any time.

So far, crews have managed to pump about 75 tonnes of fuel from the ship. Maritime New Zealand, the agency heading the response, estimates that more than 1,270 tonnes of fuel remain on board.

The Rena grounded Oct. 5 on the Astrolabe reef 22 kilometres from Tauranga Harbour on New Zealand's North Island, setting off what officials have called the country's worst maritime environmental disaster. An estimated 320 tonnes of fuel have spilled into the sea near beaches on New Zealand's North Island, killing more than a thousand sea birds.

Crews first began pumping oil from the ship Oct. 9 but quickly abandoned that effort due to bad weather.

The latest attempt has proved more complicated because of the ship's deteriorating condition — a crack now extends the width of the ship and it has a list of 21 degrees.

Captain, officer charged under maritime laws

Preparations took several days, with crews needing first to construct four wooden platforms on the side of the ship to provide a level base for pumping before the operation began late Sunday.

"This is a hugely challenging and risky operation even in full daylight," Bruce Anderson, who is heading the salvage operation, said in a news release. "These are incredibly brave and dedicated people."

About 1,290 sea birds have died in the spill. Another 207 oiled birds and three New Zealand fur seals are being treated at a wildlife centre.

The Rena is owned by Greek-based Costamare Inc. Both the captain and an officer on the ship have been charged under New Zealand maritime laws with operating a ship in a dangerous or risky manner. If found guilty, the men, whose names have been suppressed under New Zealand law, face up to a year in jail and thousands of dollars in fines.