A woman who witnessed the aftermath of a car ploughing into pedestrians at an Auckland mall says she joined other shoppers in rushing to the aid of the injured after a busy shopping day was shattered by the car crashing at speed. 

The witness said she ran to the scene at Westfield Manukau just after 1pm on Sunday after hearing a "big bang" from the nearby Coffee Club. 

She said the sound of the impact was so loud she initially thought a truck must have slammed into the low ceiling of the car park. 

She discovered it was a car that had taken out three steel bollards on Amersham Way on its way into the covered car park. 

She said one male patient was "swearing his head off" in the immediate aftermath, with another female patient conscious and three older patients unresponsive. 

Police arrested a 34-year-old woman after the incident, attended by seven St John vehicles. 

St John said four people were taken to Middlemore Hospital, one in a critical condition and three in a serious condition. 

A further person received moderate injuries and was treated at the scene. 

The woman has been charged with a driving-related offence and was taken into police custody ahead of an appearance in the Manukau District Court today. 

Police say further charges are likely. 

- Additional reporting, RNZ