"The driver swiped and hit the cars. The other cars were pretty munted."
He said the aftermath of the crash was a scene of smashed-up cars.
The worker heard the crash and immediately called for an ambulance and for a fire extinguisher.
"The car was smoking, like most cars do. Steam was coming out of it."
Fire, police and ambulance services were called to the scene to deal with the four-car pile-up.
Fire Services Jaron Phillips said the jaws of life had to free a man from one of the cars and one person was unconscious after the crash.
The 26-year-old man was taken to Middlemore Hospital with moderate injuries, said ambulance communications team leader Norman Upjohn
A second person, age and sex unknown, was treated at the scene but wasn't taken to hospital, he said.
Mr Phillips said a fuel spillage was being cleaned up at the site.
The Serious Crash Unit was at the scene, which is still closed. Motorists are being asked to avoid the area if possible.
