The person missing in Aspiring National Park is 21-year-old Hector Gastón Artigau, from Argentina, who is in New Zealand on a working holiday visa.
Artigau was hiking the popular Rob Roy Glacier Track with two friends two days ago when he fell off a rock into the river and did not resurface.
Police and local Search and Rescue members this morning resumed the search for the Argentinian national, who was last seen at around 4.30pm on Thursday, February 6, about 600 metres from the upper lookout of the Rob Roy track, near the river.
A friend who was with Artigau on the hike described the terrifying moment they saw the 21-year-old fall from the rock and into the water.
Santiago Ponce told the Herald he and another friend, Blas, were hiking the track with Artigau when they lost track of their friend.