Hai Phong has a long coastline of 125 km including the islands off the coast. It shapes a curve of Tonkin Bay, low and quite flat, muddy. In the center, Do Son sticks out like a peninsula, a key note of hills running from the mainland that are of sandstone of Devonian age. The highest peak reaches 125 m, protruding 5 km into the sea from Northwest to Southeast. The natural advantage gives Do Son a strategic marine position as well as a famous landmark with poetic beaches and valuable nursing resorts at the foot of the sandstone hills. Offshore, Hai Phong has many islands scattering across the sea, the biggest is Cat Ba Island, and the most remote island is Bach Long Vy.

Marine resources of Haiphong are rare with nearly 1,000 species of shrimp, fish including dragon shrimps, prawn, crabs, tortoise-shells, oysters, dolphins, pearls, abalone etc., and dozens of other high economic value seaweeds. Hai Phong has many fishing grounds, the largest is of high and stable reserves with over 10,000 square nautical miles in width around Bach Long Vy Island. The coastal tidal area on 12,000 acres is to fish as well as to do saltwater aquaculture and brackish water of high economic value.