The trio had been at the campsite for a week and a half after touring around Northland.
They had spent their days exploring the area and taking walks, and in the evenings playing games of 500, reading and retiring to bed, Richard Voschezang said.
However, a group of rowdy teens on the site next to theirs had been wearing Mr Smith down for days.
"Over the course of those three nights they had been told pretty much every night to turn it down but they failed to do so.
"Matt [decided to] do something about it, so at about 12.30am, he went over and disconnected the power. Then at 3am, when these guys came back from their beach walk, they found him and started screaming.
"I went across and did my first-aid ... but he was already well gone."
Mr Voschezang said he was asleep when his friend had left their tent.
"We went to bed at 10.30pm, but we couldn't get to sleep, obviously. I sort of drifted off and then [heard] Matt muttering, 'I'm going to pull the power out', so I went back to sleep."
Mr Voschezang said Mr Smith had become part of his family over the years. "I've known him for the last 15 years, pretty much every day I saw him," he said.
"Matt was the kind of person who you could sit down and talk for hours on end with. If you ever needed any help he was straight there."
The Hikurangi Volunteer Fire Brigade received a call about the tragedy at 3.10am.
Deputy Chief Fire Officer Trevor Gallagher said Mr Smith had used a Leatherman tool, which has folding blades and pliers, to cut the teenagers' cable connected to a campground power box.
"The cable initially had been taken out of the caravan socket and he had then proceeded to cut the plug off the lead.
"The irony of it is that the music was coming from a radio powered by batteries," Mr Gallagher said.
"It was a pretty drastic move to be cutting it ... It's a huge tragedy and something that should never have happened."
A young man who moved Mr Smith from the cable also suffered a minor electric shock in the process.
Camp owner Craig Stokes said he did not know Mr Smith.
"He'd been staying there a few nights with some mates. The police have got it all in hand."
A spokeswoman for the campground declined to comment. "It's all been ticked off by police."
A Worksafe New Zealand spokesman said the agency had been notified about the fatality.
Mr Smith worked at Waikato Sound and Lighting for the past five years.
Co-worker Phil Brown said he was a "pretty honest and reliable guy [who] didn't do anything crazy outside of work".
"Working in our industry, he normally would never do something like that ... It's completely out of character for him to do it. He's site-safe certified as well."
Mr Smith's brother Christopher, 24, was last night with friends at Richard Voschezang's home.
Parents Andrew and Alice Smith were too upset to speak when approached yesterday.
Their son's funeral is planned for Monday at the Horsham Downs Church near Hamilton.
