Tens of thousands of plastic bags are lining a West Coast beach after high seas ripped open an old coastal rubbish dump.

Huge damage from rough seas and king tides from ex-Tropical Cyclone Fehi ripped away the beach at Cobden Tip Head and Shipwreck Point, Greymouth,

"It is devastating," Grey District Mayor Tony Kokshoorn said.

"Tens of thousands of plastic bags are all across the beach. I have never seen anything like it.

An area about 50m back from the beach was used from the 1970s until the 1990s as a rubbish dump.

Over the years the rubbish has been blown closer to the beach, and covered up by sand.

"The dump was closed about 20 years ago, but now it has moved closer to the beach."

There was a bit of metal among the rubbish, however the biggest issue were the plastic bags, he said.

"It just amazes me, they have been in there 30-odd years, and not degraded at all."

Kokshoorn has organised a community working bee for tomorrow at 9am to clean up the area.

"The response already has been amazing. We need a really big turnout."

The weather has settled in the wider area and the focus was now on the clean-up.

Kokshoorn said at least one house had lost a roof and a hotel in the central business district could need to be pulled down as it was a safety hazard.