An elderly driver may have suffered a seizure behind the wheel when he crashed into the back of a U.S. Postal Service truck, pinning a postal worker who was sorting mail, National City police said.

The accident happened around 1 p.m. on Highland Avenue in National City in San Diego County. The horrifying 31 seconds were captured on a security camera mounted at a nearby business.

The video shows the victim's truck parked along the curb. He gets out, opens the back door and starts sorting through mail while standing at the back of the truck.

Suddenly, a car zooms into the frame, hitting the unsuspecting postal worker, the force moving the mail truck forward several feet.

As the victim tries to grasp part of the back door, his head slams against it. The postal worker appears dazed, and struggles to move his body.

His legs are pinned. He is hunched over inside the back of the mail truck.

The video then shows witnesses frantically running to the car and mail truck, trying to help. Several people surround the car and are talking to the driver inside; one man jumps into the passenger side head-first as another runs around to the driver's side and opens the door.

Sixteen seconds later, the good Samaritans are able to shift the car into reverse. As the car slighty backs up, the postal worker is freed.

He collapses onto the sidewalk.

Witness Mohammed Farha was working nearby with his nephew, Emad Farha, when they heard the sound of the crash. They were among the bunch that immediately ran to help.

"The driver was having seizures; I saw him shaking pretty badly, his foot was still on the gas pedal," Mohammed Farha said.

That was when he rushed to the driver’s side and put the vehicle into reverse. Then, he called 911.

First responders arrived and were able to apply a tourniquet to one of the postal worker's legs. The victim was still conscious and talking to first responders.

Mohammed Farha said it appeared the driver was traveling at least 60 to 65 mph when he hit the back of the USPS truck.

The good Samaritan said he and his nephew had to do something to help.

"First time I ever seen something that bad -- it was devastating," Mohammed Farha told NBC 7. "After he was hit, the wheels are still spinning. We couldn't sit there and see that."

"We just tried to keep him awake and alert, you know, focused on us not on his leg," Emad Farha added.

The USPS worker suffered major injuries to both legs. He was taken to UC San Diego Medical Center in Hillcrest, officials said. The driver of the car was also taken to that hospital.

Emad Farha said the entire thing happened in what felt like a matter of seconds.

"It happened so quick; it (was) just like, 'Wow,'" he recalled.

As of Friday morning, the postal worker's condition was unknown.

No one else was hurt in the crash.