A missing driver of one of the cars involved in a serious Northland crash that left two people critically injured has come forward.

The two-car crash occurred on State Highway 1 last night between Hautapu Rd and Nisbet St, north of the Northland town about 7.30pm.

A young boy was flown to Starship Hospital with critical head injuries, and emergency services also assisted a woman in a critical condition.

Following the crash one of the drivers had gone missing, but police confirmed this morning they had come forward and police were speaking to them.

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Crews of the Auckland Westpac Rescue Helicopter and Northland Emergency Services Trust treated patients at the scene and performed rescue operations.

Auckland Rescue Helicopter Trust communications manager Lincoln Davies said a young boy had suffered a head injury.

"He was transported by ambulance to Bay of Islands Hospital alongside our intensive care paramedic who needed to perform a rapid sequence intubation to assist his breathing," Davies said.

Their Westpac 2 helicopter relocated to the hospital, and flew the boy to Starship Hospital in Auckland.

Northland Emergency Services Trust assisted a woman who was also in a critical condition. One other person received serious injuries, and two more had moderate injuries. They were all taken to Bay of Islands Hospital.

Police said the Serious Crash Unit would be investigating.

A Fire and Emergency New Zealand spokesman said two crews attended the accident and extricated one person from a vehicle.

The other car was engulfed in flames upon arrival but was soon extinguished by FENZ crew.

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The road had been closed after the crash but had reopened at 12.45am this morning, the NZ Transport Agency said.