"The blade was at least a foot long. It was a really big kitchen knife, like in a Psycho movie.
"As he came down he held it like he was stabbing from above. I was lucky to get my hand on his wrist so I only got a slight graze on finger, then a second guy came behind me and put his arm around my neck. I leaned back and the two of us fell on the ground, that was when I got the wound to the chest.
"I had the other guy's wrists but he swapped the knife to the other hand. I knew I was fighting for my life. I had one wound, that wasn't so bad but I knew if he got me again I'd be gone.
"The second guy was trying to pull my backpack off but I had my arms out holding the guy with the knife. And I was yelling 'Help me, help me'."
The attacker fled with Bethune's cellphone. With blood pouring from his stab wound he managed to hitch a ride on the back of a motorbike to his hotel before heading to the hospital for treatment.
He said the knife missed vital organs after the blade became wedged between two ribs.
"If it had been a different angle it would have gone a long way in and would have been a different story.
"She [the doctor] said 'You're a lucky man'. When she peeled open the wound you could see the bone."
Bethune said family and friends were extremely worried but he wanted to reassure everyone that although he was a bit worse for wear he had survived the violent attack.
"I'm happy to be alive - I have a big smile on my face," Bethune told the Herald.
He said it was not the first time he had been attacked but was surprised someone would make an attempt on his life in daylight.
"I've been knifed before in Nicaragua and shot at in the Philippines earlier this year. And the team's been shot at chasing illegal gold miners. Normally it comes with the territory if you're trying to arrest someone or get them to prosecution. But this is the first time in a random robbery like this," said Bethune.
He said he normally travelled with someone but this week his cameraman was turned away at the border over visa issues.
Bethune was in Brazil trying to find out if Sir Peter Blake's death was linked to illegal gold-mining. Sir Peter was shot and killed by pirates on the Amazon River in 2001.
Despite the attack Bethune was still considering meeting with one of the prisoners convicted of Blake's murder before returning home to New Zealand next week to deliver a TEDx talk.
Macapa police are investigating the attack.
In 2010 the Auckland-based activist spent four months in a Tokyo jail after assaulting a whaler by hurling a rancid butter stink bomb during a high-seas confrontation.
He pleaded guilty to obstructing commercial activities and charges stemming from climbing aboard the Japanese ship - trespass, vandalism and carrying a knife, with which he cut the ship's security netting.
