Oil continues to spill from the container ship that has been stuck in a reef in New Zealand since last week.

The 775 foot Rena ran aground on the Astrolabe Reef, 22 kilometers off the coast of the North Island of Tauranga, on October 5, reported BBC. Maritime New Zealand also revealed that the ship was carrying 11 containers of hazardous materials, including ferrosilicon, which is can burst into flames upon contact with water. Although the dangerous materials have not fallen overboard, the threat of the ship breaking up is real, especially when stress fractures have already been found on the Rena, said New Zealand Prime Minister John Key.

"We can't rule out the risk of the ship breaking up, that's certainly being monitored," he said.

According to the AFP, the salvage work on the Rena has been stopped due to bad weather. Coastal cleanup of the pollution the oil spill has created has also been halted.

The ship was pounded by four meter high waves and 35 knot winds. The overnight disturbance forced salvage crews to abandon their work of pumping oil from its fuel tanks, said Maritime New Zealand.

It reported that around 90 tons of oil had been offloaded. About 1,200 tons more are still on board the ship. Officials have declared the fuel oil leaking from the Rena has brought New Zealand's worst environmental disaster in decades.

Around 300 tons of oil have polluted the beaches on the North Island's Bay of Plenty. About 1,300 birds have been killed, and the number is expected to go higher as the days pass by.

Minimal amount of oil spilled further from the ship and being pushed offshore by the wind, reported Andrew Berry, salvage chief of MNZ. He added that huge cracks have appeared on hull of the ship. He expects the salvage operation to go on for some time.

"Every drop of oil that we can get off the Rena is one less drop that potentially can end up in the environment," he said. "But given the huge range of variables that can affect operations, it's going to be a long, slow process."

According to MNZ, foul weather has forced it to belay more than 5,000 volunteers raring to clean the polluted beaches.

"This is a last minute change due to bad weather," it said. "Our thanks and apologies to those volunteers who were ready for action."

MNZ admitted that salvaging the Rena is one of the most difficult operations it has ever faced. AFP describes the scenario on the reef as such:

"The viscous oil has a treacle-like consistency and has to be pumped through an eight-centimetre (three-inch) pipe, with the crew ready to evacuate at a moment's notice if the ship begins to break up."

The owner of Rena, Greek company Costamare has apologized for the catastrophe. Its charterer and the world's second-largest container shipping firm Mediterranean Shipping Company will shoulder part of the clean up cost.

The New Zealand government has launched two investigations to determine how the ship hit reef, and has charged its captain with "operating a vessel in a manner causing unnecessary danger or risk."