The Hai Van Pass is an approximately 21 km long mountain pass on National Route 1A in Vietnam. It traverses a spur of the larger Annamite Range that juts into the South China Sea, on the border of Danang and Hue Province, near Bach Ma National Park. Its name refers to the mists that rise from the sea, reducing visibility. Historically, the pass was a physical division between the kingdoms of Champa and Dai Viet.