Partial ownership of New Zealand's power companies and airline will go to the highest bidder if National gains a second term in government.

National is planning to introduce a mixed ownership model for the state owned assets of Air New Zealand, and power companies Genesis, Meridian, Mighty River Power and Solid Energy.

The party estimates the partial sale will generate between $5 billion and $7 billion in three to five years, which will go towards paying down national debt.

National's plan involves increasing competition by transferring assets between state owned generators.

National candidate for Tauranga Simon Bridges says history has proven that businesses benefit from mixed ownership.

'It is very clear that businesses operate with both private and public ownership are better, more effective businesses, you just have to look at Air New Zealand, which is 30 per cent privately owned and it's a roaring success.

'Here in Tauranga you have the Port of Tauranga and TrustPower, both are partly privately owned.”

Under National, proceeds from the sale of assets will go into the new Future Investment Fund to be used to purchase new schools and hospitals without having to borrow from overseas lenders.

'By doing this we are able to invest in the future without having to borrow, if Labour does not do this it will still have to find the funds from somewhere – it will be borrowed from overseas.”

Both Labour and the Green Party have hit out hard against the sale of assets.

Labour candidate Deborah Mahuta-Coyle says Labour is absolutely against the sale of New Zealand assets.

'John Key has made it quite clear that National cannot guarantee the 49 per cent of sales will not end up in foreign ownership.”

Deborah says the estimated $7 billion National intends to make from asset sales will be spent three times over by the political party.

'They will be spending three times the amount in paying down debt, farmers' irrigation and funding for schools – there is only so much money.”

If state owned enterprises were to be sold, first option to buy is for New Zealanders with National expecting 85-90 per cent of ownership to remain in the hands of Kiwis.

However, Deborah says many Kiwis cannot afford the cost of living, let alone purchasing shares in power companies.

'It makes no sense. Everyone remembers when we sold our state assets in the 1980s and we know we shouldn't repeat the mistake.

'People are struggling and cannot afford to buy shares – it won't be ordinary Kiwis buying shares.”

Simon says New Zealanders are looking for safe quality investments and will take the opportunity to invest in state assets.

'We accept that not every New Zealander will be able to purchase shares, but many Kiwis will.

'We are not going to hock assets the way Labour did in the 1980s as trade sales – we will keep the majority control of 51 per cent.”

National says it is committed to returning the country to surplus by 2014-15 and to do so will put a cap on government spending to $800 million in 2013 and 2014 and $1.2 billion in 2015.

Instead of selling off these companies, Deborah says Labour will pay off the country's debt by introducing a capital gains tax, which she says will generate $78 million in the first year.

Debt will also be paid off through an increase in the introduction of the Emissions Trading Scheme by 2014 under Labour.

Green Party Tauranga candidate Ian McLean says ETS is a key part of Green Party policy and will look to revoke the current $2 billion a year in government subsidies to businesses.

'We have now identified the businesses that are producing pollution and we need to put a price on that pollution.

'Agriculture is one of the biggest carbon emissions industry, we need to bring it into the ETS.”

When it comes to the sale of power companies, Ian says the government is 'crazy” to sell.

'If you have a profitable business, you have something that is working and generating profits you would be crazy to sell it. You should not be focusing on the income from the business, but on the capacity to take the business further.”

Labour's changes to the tax policy will see people earning more than $150,000 a year face higher taxes, which will also contribute to paying off debt, says Deborah.

'We have the same goal as National to be back in black by 2014 – up front Labour will borrow more at the start to do so, but will pay it off in the same time.”

Deborah says people will face higher power bills if power companies are privatised.

'It is important we remain in control of these companies to control the price and dividends – and in case of any emergency.

'If there is a black out, we need to know we have control.”

New Zealand First candidate Brendan Horan says the government needs to be asked about what share of state assets will be sold and who they will be sold to, before a decision is made.