The Hague (AFP) - The Netherlands on Tuesday unveiled a multi-billion-euro, multi-decade plan to counter the biggest environmental threat to the low-lying European nation: surging seawater caused by global climate change.

The project, expected to span 30 years and cost 20 billion euros ($25 billion), will see new sea barriers built and existing dykes strengthened in the country, much of which lies below sea-level.

Environmental Minister Melanie Schultz van Haegen, presenting the plan to parliament, called it "a new chapter in the history of our centuries-long relationship with water".

The need to protect the Dutch from the looming threat meant "it's time for a new... plan with extra protection," she said in a statement.

The government said it was aiming to have the whole country ready by 2050 to face the effects of climate change.

"We are safe, but our delta remains vulnerable," it said in the statement.

For centuries, the Dutch have battled the waters of the North Sea that have at times flooded large swathes of the country, particularly in its southwestern Zeeland province.

After a disastrous flood in 1953 which left almost 2,000 people dead in Zeeland, the Dutch built a system of dams, storm surge barriers, dykes and other water-management projects, known collectively as the Delta Works, to keep the sea out.

But a growing population, growing industry and climate change have necessitated a "new Delta plan," Schultz van Haegen said as she unveiled the details in The Hague.

A study by the Dutch National Environmental and Living Institute, released last week, showed one in three dykes or dams did not comply with current safety standards.

"Looking at the disasters that can hit the Netherlands, a flood will have the largest impact on society," the report warned.

Part of the government's plan will see some 200 dykes reinforced, better usage of fresh water, and making cities more "water-proof", for instance by introducing floating homes and creating space for water to flow.

In the Rhine and Maas River deltas in the southwest, the government was looking at building stronger dykes, while surge barriers were to be fortified.