Joanna Lam, 24, and Connor Hayes, 25, were last seen at Fox Glacier on the afternoon of Sept. 10, according to police.
Lam failed to show up for work Sunday at The Ottawa Hospital's Civic campus, a friend told CBC News.
"A portion of their wrecked rental van was located earlier today [Tuesday] in a gorge off the Haast Pass road at Haast Gates on the west coast of the South Island," police said in a news release.
"The rear wheels and chassis of the vehicle were located about 80 metres down a bluff in the Haast River. The body of the vehicle and engine have not yet been located."
Police don't yet know whether Lam or Hayes was inside the vehicle when it left the road.
Investigators are analyzing the crash site while searchers in boats and on foot will make their way up the Haast River. A helicopter is also involved in the search.