Deputy chief fire officer Michael Ross, of Dargaville, said as soon as they arrived at the scene police asked they urgently give medical help to the injured.
"There were people lying on the road beside the vehicle. Members of their family were comforting them, as they had been travelling in convoy."
Firefighters began to free three people trapped in the car that was pinned in the large tree. It involved removing the doors on one side.
One person with moderate injuries was flown by helicopter to Whangarei Hospital, while three others were taken by St John ambulance to Whangarei with minor injuries.
Mr Ross said there had been previous fatal crashes on the stretch of road, plus plenty of injury and non-injury crashes.
He said as they worked under lights to free those trapped, a cross nailed to the tree above the damaged vehicle brought the situation home.
"It was pretty eerie," Mr Ross said.
Police confirmed the cross marked the death of a 39-year-old Dargaville man, who died in December 1997 following a crash in the same area.
The police Serious Crash Unit was investigating Monday's crash and will consider what charges, if any, may be laid against the driver. As a matter of course the vehicle would also be examined.
"Police extend our sympathy to the families of those involved and our thoughts are with their loved ones at this tragic time," Mr Ewers said.
"Crashes like this are preventable and we all need to do our part to reduce deaths and injuries on our roads."
The fatalities bring Northland's road toll to 18.
Eleven people died over a harrowing Queen's Birthday weekend - the worst road toll for the holiday in 27 years.
New Zealand's worst ever Queen's Birthday weekend on the roads was in 1973, when 24 were killed.