They are also investigating whether 25-year-old Connor Hayes and 24-year-old Joanna Lam may have somehow driven off the road.
A spokeswoman for Tasman Police told The Canadian Press early Wednesday that an investigation will establish what happened.
The couple were last seen Sept. 10 at Fox Glacier, a popular tourist destination.
They were reported missing by a family member in Canada on Monday after Lam didn't show up for her first day of work at the health board in the city of Nelson.
Police crews along with volunteers searched the Haast River area for the couple Wednesday, but were unable to find any trace of them.
The couple's wrecked rental van was located Monday in a gorge and more debris believed to be from the vehicle have washed up on a beach seven kilometres away.
Police say a helicopter with heat-seeking equipment will join the search Thursday. A search dog is also being brought in from Christchurch to assist the ground teams.
Meanwhile, Foreign Affairs says Canadian consular officials are working closely with local authorities.
"Consular officers remain in contact with family members and are providing assistance," said spokesman Ian Trites.
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