Despite the rough, remote landscape, authorities say they're trying to stay positive in their search for 25-year-old Connor Hayes and 24-year-old Joanna Lam.
"There has been some pretty heavy rainfall and slippage and road damage in that area in the last couple of weeks. The terrain is pretty harsh," Barbara Dunn, a spokeswoman for the Tasman District New Zealand Police told The Canadian Press.
"In terms of the outcome of the search we're keeping an open mind at this stage as to what might happen to them and where they may be."
Hayes and Lam were last seen on 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 heath board in the city of Nelson.
Police were making inquiries about the couple when an officer in the Haast Pass area — about a five-hour drive from Nelson — spotted parts of a vehicle in the river.
"It was about 80 metres down below the road in the Haast River. That portion was essentially the chassis of the vehicle and the wheels," said Dunn.
"The body of the vehicle, the engine and any other part were not there."
Police have said they don't know if Hayes and Lam were in the vehicle when it went off the road, but that the parts found in the river were matched to a van they had rented.
A "fair number of people" — including police and volunteers — are now out searching for the pair.
"We are sending ground searching teams on foot...We've also got a jet boat going up the river and a helicopter flying over to see if there's any sign of the pair," said Dunn.
A police crash investigator and photographer have already been to the scene where parts of the van were found.
The Foreign Affairs department 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.
Friends of Hayes and Lam have taken to Twitter to voice their support for the authorities who are looking for the pair.
One man, who identified himself as a friend of Lam's family, set up a webpage where people could show their support for the search efforts and keep the pair's story in the spotlight.
"Joanna Lam and Connor Hayes are loved by many back home in Canada. Friends and family are desperate to have them found and home again," the webpage said.
"The work of the Search and Rescue team in New Zealand is greatly appreciated. Our thoughts and prayers continue to be with them."
_ By Diana Mehta in Toronto.
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