Penny Madden's home in Hector, on the West Coast of the South Island, has been flooded three times this year.

A leaked government report calls for immediate action to help protect thousands of people and $19 billion of property at risk from increased flooding and coastal erosion.

The report, commissioned by the Ministry for the Environment, was delivered in April but has still not been officially released.

It concludes that $19 billion worth of buildings, about 43,000 homes, 130,000 people, five airports, more than 2000 kilometres of road and 46km of railway face "higher levels of coastal risk exposure" as a consequence of rising sea levels.

ALDEN WILLIAMS/STUFF Granity on the West Coast is a victim of coastal erosion in New Zealand.

"Sea level will continue to rise for at least several centuries, posing an ongoing challenge for managing the transition to more sustainable coastal communities, both globally and locally," the report states.

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"Planning for adaptation at the coast needs to start now" and cannot wait for uncertainty about the exact impact of climate change to be resolved, it says.

RICHARD ARLIDGE Severe coastal erosion at Punakaiki's Beach Camp on the West Coast.

"Waiting until uncertainties are reduced before making decisions, or doing nothing, is usually not viable or acceptable to those most exposed to the risk".

It concludes that a modest sea level rise of about 40cm would mean that "present day, rare storm-tide" floods could occur on average once a year.

The report was leaked to the Green Party this week. Co-leader James Shaw claimed the Government was deliberately keeping the report secret.

"This is an extraordinary report. We need this information to be out there," he said.

"By keeping this report secret, they are removing the opportunity for families and businesses to plan.

"They want to pretend that climate change is not a big deal."

Shaw said the Government need to act now to help people and properties at risk before uncertainty over the impact of climate change was resolved.

"There is too much risk and we can't wait for the uncertainty to be resolved. It will have happened by then and we will have lost all those buildings.

"The way to reduce the risk is to start planning and adapting now."

Penny Madden's West Coast property has been flooded three times this year. The sea has been moving closer to her home in Hector for many years, eating away at metres of shoreline. She wanted the Government to help people affected by climate change.

"I am not sure there is a lot they can do, but financial assistance to help people relocate would be nice, but I can't see that happening.

"Bill English says that global warming isn't an issue in New Zealand, which is quite ironic. People on the West Coast know it is an issue and have seen it for years."

A second report on climate change commissioned by the Government will also not be released until after the election.

Deputy Prime Minister Paula Bennett has received the first report produced by the climate change adaptation technical working group, tasked last year with presenting options for New Zealand to adapt to climate change.

The group consists of 10 experts across science, academia, industry and governance groups.

Bennett confirmed she had received " some early advice from the group", but the report would not be released until it was complete.

"The draft final report is due in November and then the final report in March."

The documents would be released once the final one was complete.

A spokesperson for Environment Minister Nick Smith did not immediately respond to calls for comment.