Leader of the Opposition Simon Bridges says National will reverse a ban on offshore oil and gas exploration if it comes into power in 2020, describing it as "a wrecking ball" for regional New Zealand.

Bridges, a former Energy and Resources Minister, also warned the ban would threaten gas reserves and eventually make New Zealand have to import coal to power its industries and homes.

"We've got a decade or under of gas left, and that's what runs much of our heavy industry in the Northland, but also through to the shops and the homes," Bridges said.

Speaking to reporters in Auckland, the National leader said the ban made neither economic nor environmental sense.

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It did not amount to a transition away from fossil fuels because it was halting exploration "in pretty short order", he said.

"What's going to happen here is international investment will literally dry up from now.

"If you're a business in New Zealand in this sector you're not going to do more and so you will see job losses follow reasonably quickly."

The policy would "send a chill down the spine of NZ business" following Government moves last week which affected the irrigation sector and also came after little consultation.

New Zealand signed up the Paris Agreement to curb greenhouse gas emissions under the National-led Government. Asked what he would do differently to combat emissions, Bridges said he would investigate a Climate Commission and pricing mechanisms, and reduce transport emissions by growing the electric car fleet.

"To just pull the rug out, to kill a sector like this, take a slab out of the economy quite quickly, that's definitely not the way to go."

National would reinstate the Block Offer process which allowed oil and gas companies to tender for exploration permits each year.

When it was pointed out that the popularity of Block Offers was waning, he said that was the result of a low oil price, which was now rising again.

Bridges also took aim at NZ First, saying the party should "hang their heads in shame" for supporting a policy which affected its core support base in the regions.

Energy and Resources Minister Megan Woods said Bridges' promise to reverse the ban was "irresponsible".

"Communities like New Plymouth and Taranaki need a strong a clear plan for their future and that's what we're providing."

In announcing the new policy, Labour said it was confident that there was additional gas supply within existing fields and that households which ran on gas would not be affected.

Woods said there was 10 years' worth of gas under already-consented reserves, and additional supply from any gas discovered in existing permits.

She said the Barque field off the east coast of the South Island was estimated to contain 11 trillion cubic feet of gas.

"If your house is heated by gas, it will be tomorrow. It will be next year and the year after."