The area dedicated to marine reserves has grown by half, with five new reserves for the West Coast.

Conservation Minister Nick Smith has formally approved the new the new Kahurangi, Punakaiki, Okarito, Tauparikaka and Hautai reserves, totalling 17,500 hectares.

He says it is a major step forward for marine conservation.

Mr Smith says the reserves will enhance understanding of the region's unique marine habitats and complement the adjoining protected areas on land.