Nick Bennett, from Mackay, Queensland, suffered a head wound in the attack. He told ABC radio: "This wasn't just a quick hit as you would expect from a robbery. This was wanton butchery."
Guides Kuia Kerry and Matthew Lasong were killed when six bandits armed with machetes, a rifle and a home-made gun attacked the group as they camped along the Black Cat Trail in PNG's Morobe Province on Tuesday. Seven Australians and one New Zealander survived, and returned to Cairns on Thursday.
"I've seen some things in my life [but] this was too graphic to describe," said Bennett.
He lauded the bravery of trek leader Christie King, who put herself forward when gang members demanded to talk to the "boss man" while their henchmen attacked other hikers and slashed tents with their machetes.
"I'm on my elbows just bleeding out. They've hit another one of our guys who was in his tent. He's come out to see what's going on and they've clubbed him over the head," Bennett said.
"And then they've taken to the tents with machetes and to our bags, just dragging bags out. They're demanding money, which we gave them. And Christie stood up when they called for the boss man. I don't think they realised that she was a woman."
PNG's prime minister, Peter O'Neill, has warned that those responsible face the death penalty, and says the incident has harmed his nation's tourist industry.
Bennett's voice broke as he described the horrific scene the gang had left before fleeing into the bush with money, cameras and passports.
"The sight was just appalling," he said. "Some of the boys had escaped into the bush and when they came back out you could see the shock on their faces. The site was like a war zone. It was just terrible."
He described how the injured Australians had to trek for five and a half hours towards the nearest village, following the track of the fleeing bandits and fearing another ambush.
He said the group managed to call the trek leader's Papuan husband, who immediately mobilised medical teams and organised for villagers to start heading up the track.
"We were walking in the dark out of the jungle. Three hours down we encountered the first villagers making their way up, armed with bush knives.
"Once they understood what had happened they really didn't talk too much to us. They just said 'sorry, sorry'." [TheGuardian]