St John confirmed three people were dead, including two children, and two others were seriously injured after a car crashed into a truck.
Huntly Volunteer Fire Brigade chief fire officer Craig Bush said the deceased were an adult male and two young boys.
Firefighters assisted a woman and 9-year-old girl who were injured in the crash out of the vehicle.
Both had sustained serious head injuries, Bush said. They were airlifted to Waikato Hospital.
"It has been a pretty rough day. We were also called to assist ambulance at a cardiac arrest and the person died so that was four people dead in our little town in an hour and a-half," Bush said.
Counselling would be offered to any firefighters who needed it.
"We're able to offer all the support in the world for anyone who needs it."
The woman's condition was initially assessed as serious but was upgraded to critical on the flight.
A St John spokesman said they were called to the crash, understood to have happened near the Essex Arms pub, at 2.36pm.
Waikato road policing senior sergeant Andy Bubear said at 2.30pm a southbound car carrying five people had crossed the centreline and collided with a northbound truck.
Three people had died. He said diversions would be in place for some time and urged people to be patient while police investigated.
"I also urge people to drive to the conditions. If your tired or fatigued stop."
The Mark Grey Carriers truck involved in the crash had some damage to its front.
Company director Mark Grey said the truck driver was uninjured.
"We're not doing too well. I'm supporting the driver and we're giving the police as much information as we can."
Some residents did not want to speak about the crash out of respect for the people involved.
A local shop worker, who asked not to be named, said customers had been coming through talking about the crash and supporting each other.
"There was a whole commotion at the time and there were helicopters up.
"It's a triple fatality, so we're expecting emergency crews to be around for a while. We don't know if [the victims] are locals or not, but it's a sad thing for the community.''
Waikato District mayor Allan Sanson said the community would be rallying to support one another.
"Our thoughts and hearts are with the family, obviously. I understand there is three departed and two in critical care. I don't know if they're a family or connected in anyway, but I'm assuming there is a family in there,'' he said.
"Unfortunately we live in a part of New Zealand which has huge traffic numbers and occasionally we have these types of things happen for whatever reason.
"Every time there's a truck and car involved, usually the occupants in the car come off second best."
It was not yet known whether those involved were a local family, he said.
"But if they are local people, it will impact even more in the community. It is a hard one. My heart goes out to the family - it really, really does.
"It happens and people don't get to have their goodbyes - they don't get to have that last cuddle, they don't get to have that last kiss. It's just that sudden gone - like somebody turning a light switch off."
The three deaths would take this year's official road toll from 229, where it stood today, to 232.
The toll for the same period last year was 10 fewer.
