About half a dozen clients at the Village Headcourters on Napier Road scattered as the black hatchback rammed through one of its walls about midday.
The woman driver, aged about 40, was taken to Hawkes Bay Hospital's emergency department with minor injuries, a central ambulance communications spokeswoman said.
Salon co-owner Coreen Russell said the crash "sounded like a bomb".
"You just didn't know what it was, you could just hear this terrible noise...and then all you heard everything smashing and breaking, you didn't know if it was an earthquake or what.
"Everyone just had to scatter."
She was still shaken by the incident.
"It's a miracle nobody was killed."
The salon's other co-owner Ange Davies said the damage to the business was extensive.
"The whole back door's all smashed and a wall's smashed in and the counter is smashed through and the waiting chairs are smashed."
Police would be interviewing the driver and witnesses, as well as checking the condition of the car, Ms Davies said.
The salon's clients were sent to another salon where their hair was finished, she said.
Insurance assessors were yet to inspect the damage.
