More than 3,000 people in New Zealand have now volunteered to help clean up the oil-soaked beaches off the once-pristine Bay of Plenty.

The ship Rena has been stuck on a reef near Tauranga since last week, spilling tonnes of oil and containers into the sea.

About 1,000 birds and other wildlife have been killed in what officials say is the country's worst maritime disaster.

Other birds, including penguins, are covered in oil that has leaked from the ship, while debris including deer skins and half-cooked burger patties have began washing up on the beaches.

Volunteers have been working day and night to help clean up the beaches. More than 220 tonnes of waste, including oil and debris from the ship, have been cleared.

Residents say the beaches are looking cleaner as the winds are now blowing oil out to sea, allowing clean up teams to make progress.

"It's much better than it has been, not that much oil is coming [on shore]," said resident Liz Bridgeman.

"We seem to be getting on top of it."

But the government has warned residents to prepare for weeks - maybe months - of pollution.

The ship is holding itself together because of its position in the reef and the ship is still in a precarious position.

ABC reporter Mark Douglass says massive fissures run down the side of the ship and it is now a matter of when, not if, it will break in half.

"It is on a 22 degree tilt at the moment. It is making it difficult for salvage crews to actually get on board safely," Douglass said.

"The clean-up operation is underway - the salvage experts are hoping that the calmer weather that they have in the next couple of days will allow them to remove more of those containers and start working on what is going to happen when the ship breaks."

Crews are working against time to try to find ways to get the hundreds of tonnes of fuel off the ship.

Good weather allowed teams board the ship on Friday.

Maritime New Zealand's Bruce Anderson is optimistic the pumping of oil from the stricken ship could start soon.

"If the weather stays fine and all goes well they might be able to start transferring oil from [Saturday]," he said.

The 47,000-tonne ship, owned by Greek company Costamare Shipping, was heading towards Tauranga from Napier when it ran aground off the North Island last week.

It was carrying 1,700 tonnes of fuel and more than 1,300 containers.

As much as 350 tonnes of oil has spilled and 88 containers have fallen overboard, affecting shipping lanes and leaving debris washing ashore on nearby beaches.

The ship's captain and second officer have been charged and remanded on bail, accused of operating the ship in a dangerous manner.

Beaches along New Zealand's Tauranga coast have been closed due to health concerns as oil washed up on shore.

ABC/Reuters