A second person has died in hospital following a head-on crash on State Highway 16 at Waimauku on Wednesday.

The horrific accident between two cars saw two women suffer critical injuries.

A 64-year-old woman died in Auckland Hospital later on Wednesday evening.

Yesterday a second woman died in hospital from her injuries.

Police are continuing to investigate and would like to hear from anyone who may have seen the crash, which happened around 5.15pm just north of McPike Rd on State Highway 16.

Motorists watched in horror as emergency services pulled people from the wreckage of the accident near Waimauku last Wednesday. Photo / File

The Auckland Westpac Rescue Helicopter was tasked to assist emergency services in transporting a woman in a critical condition to Auckland City Hospital after the accident.

The woman, who was in her 20s, needed a rapid sequence intubation to assist her breathing and a blood transfusion was administered by a Helicopter Emergency Medical System doctor.

Ambulance staff pulled victims out of the wreckage - but two women have now died from their injuries. Photo / File

Two other people were injured. One was reported to be in a serious condition and the other moderate.