The trio were stopped on their way by a roadblock set up by six people, now being hunted by police, the Papua New Guinea Post-Courier reported.
The six suspects were armed with knives and axes and set up the road block near Rondon Ridge Lodge, 40 minutes outside of Mt Hagen and surrounded by rainforest.
The three tourists were robbed of all their belongings including cash in kina [PNG dollar] and Australian and New Zealand currencies.
During the robbery, Monteath sustained knife wounds while struggling with the thieves.
He was rushed to Mt Hagen general hospital and discharged that same day, June 5.
The two other Australian tourists robbed escaped injury after one managed to disarm one of the thieves of their axe.
"The incident was an unfortunate one today but there are bad people all over the world," Australian Greg Mortimer told the Papua New Guinea Post-Courier.
Police were called soon after the six thieves fled and local community leaders and councillors managed to retrieve most of the stolen belongings.
PNG police are now working with those same community leaders councillor Willie Wingti and Bakri Komp to find the six suspects involved in the attack.
Western Highlands police commander Jacob Kamiak said four investigative officers were on the case searching for the criminals.
Trans Niugini Tours owner Bob Bates, who runs Rondon Lodge where the victims had been heading, said nothing like this attack had ever happened in the 13 years of their operation.
"It is just disgusting that the elderly tourists would be attacked the way the three men were," Mr Bates said.
Based in Christchurch New Zealand, Monteath is a polar and mountain photographer who has been taking international geographic photos for magazines and books since 1973.
He has undertaken 21 Himalayan expeditions and has climbed New Zealand's highest peak, Mt Cook, 13 times.
