Emergency responders are expecting oil to wash ashore at Western Bay of Plenty beaches, south of Mount Maunganui from Wednesday.

The heavy fuel oil emanates from the leaking container ship, Rena, which grounded on the Astrolabe Reef at 2.20am on Wednesday.

Oil emanating from the container ship Rena stuck on Astrolabe Reef is expected to wash up on Western Bay of Plenty beaches from Wednesday.

Maritime New Zealand national on scene commander Rob Service says an approaching storm is expected to upset the emergency response and cause more oil to spill into the water.

'As a result of that we can expect oil on the beaches.”

He says 'predicting where the oil is most likely to be is not an exact science,” but Papamoa Beach is a likely spot.

Prime Minister John Key described the pending beach clean-up as a 'bucket and spade” operation, but responders are pleading for the public not to attempt the work on their own.

'It has to be organised and undertaken by people with skills and knowledge,” says Rob.

Not responding with the necessary care could result in making the pollution worse.

'It's not just as simple as scooping it up.”

Maritime New Zealand is seeking volunteers to be trained to correctly clean-up the beaches, to work in conjunction with 250 trained staff who are on standby.

'If people want to volunteer and particularly organisations of fit and able bodied people want to, call us.”

The number to call to offer voluntary help, or for oil pollution sightings is: 0800 OIL SPILL or 0800 645 774.

Maritime NZ has confirmed eight containers on board Rena contain toxic substances, with four containers holding ferrosilicon, a hazardous substance that is flammable when combined with water.

Rob says these containers are designed for seavoyages and remain in tact. Plans are underway to remove them from the ship.

Two other containers hold hydroperoxide, and a further two contain unnamed chemicals, both are classified as low toxicity.

John Key, speaking in Tauranga today following an aerial inspection of the Rena wreck site, said there are 500 New Zealand Defence Force staff on standby.

The beach clean-up operation will be just one arm of the overall ship salvage and recovery operation and it may take some time for emergency responders to commence it.

'We are prepared for shoreline clean-up and we will do it. I promise you. We won't do it immediately, but we will do it,” says Rob.

A possible method to prevent oil from washing up on the beaches is the use of booms, but Rob says it was not an effective option in this instance.

'If we could have boomed the ship, we would have done it.”

He says it was not possible owing to the wave action, strong currents and deep water around Rena as these factors made it too dangerous for responders to work.

He also says booming is typically ineffective.

'In most instances of where booming is used only 10 per cent of the oil is caught.”

Operations are underway to pump the 1700 tonnes of fuel on board Rena off the ship.

About 100 tonnes of fuel is believed to have leaked into the ship's keel duct and Rob says it is this oil that will leak into the sea during the approaching storm.