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A dairy worker pulled an injured truck driver from the wreckage of his cab moments before a second big rig laden with 33,000 litres of diesel erupted in flames.
Explosions rocked the surrounding area shortly after the fire broke out, and a plume of thick black smoke drifted over Hamilton.
Fonterra driver Ted Collins was following the northbound Freightlines truck on State Highway 1, and saw it collide with the Shell diesel tanker at Horotiu, north of Hamilton.
"The fuel tanker heading south got into trouble and jack-knifed across the road and on to its side. The guy in front of me didn't have much time to do anything and didn't quite stop in time."
The Freightlines truck, driven by a 51-year-old contractor, ploughed into the diesel tanker, Mr Collins said.
"With 40 tonnes you've got a bit of momentum, and he had almost stopped when he hit it."
Mr Collins leaped from his cab and ran to the aid of his fellow truckies.
"I did what I could to save somebody, it's a natural instinct."
Senior Hamilton fire station officer Daryl Trim said Mr Collins' actions were heroic.
"It's fantastic. If he hadn't done that, it may have had some dire consequences. It's pretty heroic really."
Mr Collins said: "I didn't really think about it, I just knew one of my truck friends could be dead or dying. It was a fuel tanker and I thought I've just got to get there quickly."
Mr Collins approached the Freightlines truck's cab as the dazed man was getting out of his seat, struggling to get away.
"The other truck driver I could not get to - his truck was ablaze and it was blocking the road, there was no way I could get to him.
"That was the thing that was worrying me. I thought the other guy had gone, it was a hell of a blaze."
Mr Collins helped the injured man to the side of the road, away from the fire.
"He was slightly out of it, a bit hurt. We sat down for a few minutes then some big bangs hit. I could see fuel going into the drains at the edge of the road and thought it [the fire] might get to us, so we had to move along another 50 yards or so."
The 28-year-old tanker driver escaped from his cab on the other side of the blaze with minor injuries.
Both drivers were taken to Waikato Hospital. The tanker driver was discharged, but the Freightlines driver was admitted with moderate injuries.
Those battling the blaze faced temperatures of up to 1000C. The fire gutted both trucks.
Gavin Crook, who lives metres north of where the crash occurred, said he heard a loud bang, followed by the sound of cars slowing down.
"It was like a bomb, and a big amount of smoke and flames were coming out. You could feel the ground shaking."
The accident closed SH1 between Hamilton and Ngaruawahia.
Transit spokesman Chris Allen said the highway surface was badly damaged, and a 70m stretch had to be rebuilt and resealed during the day at a cost of about $20,000.
