LOUISVILLE, Ky. (WDRB) -- A semi truck filled with gasoline caught fire in Rockcastle County, Kentucky, Sunday, and witnesses say the only reason the driver is still alive is an anonymous hero who wouldn't give up until he was pulled to safety.

Flames shot into the air and thick, black smoke billowed from the semi truck that was carrying 8,000 gallons of gasoline that bystanders say was ready to blow at any second. The truck crashed about an hour south of Lexington, and diesel inside sparked massive flames.

The truck driver was trapped inside -- but a man out of nowhere stepped in to help him.

"The guy who crawled in the truck is a hero," said Sam Hamilton, who witnessed the fire. "That guy is amazing. I mean, he wasn't leaving without him. I mean, if he would have died, he would have died."

"To see him stay in there -- and it was getting hotter and hotter, and everybody up here was yelling, 'Get out!' because the tires were actually exploding," Hamilton added. "They thought it was the fuel, but it was actually the tires. That part was pretty safe. The guy stayed in there the whole time, he wasn't leaving without him."

Police say that, after the rescuer helped free the truck driver, he simply drove away.

"He left," said Hamilton. "We don't even know his name."

"I wish I could have shook his hand and said, 'Thank you' myself, but when he was done, he just left," Hamilton added.

Hamilton summed the whole experience up in four words:

"God was with him."

No word on what caused the crash.

Copyright 2018 by WDRB News. All rights reserved.