Salvage crews have called off another attempt to pump oil from a cargo ship stuck off the New Zealand coast due to rough weather. Experts think it's just a matter of time until the ship breaks apart.As 4-meter (13-foot) waves battered the cargo ship Rena stranded off New Zealand's North Island, a three-man salvage crew was again forced to abandon efforts on Tuesday to pump oil from the ship.The team was able to remove about 90 tons of heavy fuel oil from the ship over 29 hours, after pumping 11 tons in a previous attempt.Some 1,300 tons of fuel remain on board, however, while another 350 tons have already spilled into the sea.Some experts say the container ship could break up at any time. Maritime New Zealand confirmed a width-wise crack on the Liberian-registered Rena, but also stated it's been in the same position since last week.The Greek-owned ship struck a reef 14 miles (22 km) off Tauranga last Wednesday, off the east coast of New Zealand's North Island.The leaking oil has already started washing up on pristine shores, killing some 1,300 seabirds. Around 200 birds and three seals are currently being treated at a wildlife center.More than 5,000 people have volunteered to help clean the beaches there.Rena's captain and first officer, both from the Philippines, face jail time and fines for charges of reckless piloting.Mediterranean Shipping Company, which leased the ship to transport cargo, claims liability for the cleanup, which so far has cost more than 2 million euros ($2.7 million), lies with ship owners Costamare Shipping Inc.Costamare last week issued a video apology for the accident.New Zealand Transport Minister Steven Joyce said chances are not realistic to get all oil off the ship before it breaks up and sinks. "I think it's a case of getting everything off that you can," before the weather shifts, said Joyce.New Zealand's environment minister has called this the greatest catastrophe in the country's history.