An Auckland-based company has applied to mine 12,000ha of seabed off Waihi Beach.
Pacific Offshore Mining said it plans to look for gold, silver and ilmenite, an important source of titanium, in an area parallel to the beach, about 2km from shore.
Coromandel Watchdog spokesperson Ruby Powell said the project threatened the surf break at Waihi Beach, and had the potential to increase erosion of the coastline south of it.
Even if the permit was granted, the company would still require resource consent from the Bay of Plenty Regional Council.
No offshore exploration permits are currently operating off the east coast of the North Island.