(CNN) -- A major clean-up operation is underway along the north coast of New Zealand's North Island as debris and oil leaking from a cargo ship that ran aground on a reef wash ashore, officials say.
The Rena, a Liberian-flagged vessel, struck the Astrolabe Reef, about 12 nautical miles off the city of Tauranga, last week.
New Zealand's oil spill response agency, Maritime New Zealand (MNZ), estimates that as much as 300 tonnes of fuel oil has leaked from the vessel, which was carrying 1,700 cubic meters (450,000 gallons) of fuel.
The country's environment minister, Nick Smith, has called the spill New Zealand's most significant maritime environmental disaster.
As of Friday, clean-up teams collected 95.45 tonnes of solid waste and 6 tonnes of liquid waste from beaches in the Bay of Plenty, MNZ said.
About 60 kilometers of coastline, from the towns of Maketu to Mount Maunganui, is contaminated with oil, the agency said.
Pubic access to some waterfront areas has been restricted due to health concerns.
"We are now coordinating a team of around 1,000 people involved in operations on land, sea and air and covering areas like field operations, planning, logistics, wildlife recovery and community and iwi [indigenous Maori people] liaison," said National On Scene Commander Nick Quinn.
MNZ said that 500 dead birds have been found following the oil spill.
The agency said 140 people scoured the coast yesterday for wildlife affected by the spill and 51 oiled animals are being treated at a center that has been set up in Tauranga. A team has been established to capture seals and five of the animals are being kept in captivity.
Greenpeace has expressed "extreme concern" about the spill and urged the government to avoid using further toxic dispersants.
"This is an unfortunate illustration of just how difficult it is to deal with oil spills at sea," the organization's Steve Abel said.
"Even a slow and relatively accessible oil spill like this one has clearly stretched New Zealand's response capability to its limits," he said.
"It is also a potential disaster for the blue whales and dolphins presently calving in the area, as well as numerous other marine species."
MNZ said that 88 containers had fallen off the ship, 20 of which have washed ashore. Due to the hazard the containers pose to shipping, the agency said navigational warnings had been issued and major maritime traffic has been re-routed.
The Rena has suffered substantial structural failure and there is a concern that the stern of the vessel may break up, MNZ said.
Salvage teams have three tugs mobilized either to hold the stern on the reef while efforts continue to remove oil from the ship, or to tow the stern to shallow water to extract the oil, the agency said.
Containers remaining on the vessel continue to move, making it dangerous for salvage crews to work on board.
Salvors have worked to build a platform to attach to the side of the vessel today to be used to assist fuel recovery operations, MNZ said.
The ship's second officer appeared in Tauranga District Court yesterday to face a charge of "operating a vessel in a manner causing unnecessary danger or risk," MNZ said.
The Rena's captain was remanded on bail on Wednesday on the same charge, on the condition he surrender his passport. His name has not been released.
If convicted, they face a maximum fine of $7,800, or up to 12 months imprisonment.
CNN's Karen Smith and Laura Smith-Spark contributed to this report.