GREENFIELD, Ind. -- More than two dozen passengers escaped a fire on board a Greyhound bus in Hancock County early Monday morning.

The bus, bound for Indianapolis from Columbus, Ohio, caught fire at about 3 a.m. along Interstate 70 between the Greenfield and Mount Comfort exits, 6News' Julie Pursley reported.

Slideshow: Fire Scene
Video: Passengers Detail Massive Bus Fire

Passengers said that about an hour before the fire broke out, they heard a pop. As the bus passed Greenfield, passengers started noticing smoke and told the driver about it.

"All of a sudden, it started smoking, and then everybody starts yelling that it was on fire in the back," said passenger Shelton Woods, from Ohio.

The driver pulled over, and flames began to spread throughout the bus.

Everyone got out of the bus safely, but it wasn't easy. Some passengers had to climb out of windows.

"It was disarming, like, I was asleep," said passenger Sandy Peters.

Spc. Dustin Hancock, who served in Iraq and was on the bus, jumped out a window and ran around to the front of the bus to pull the front door open so more passengers could get out.

"It's probably one of the most intense things I've been through in my life," said passenger Marianne Louise Rector.

Passengers said the bus driver also helped everyone get out.

"Passengers always panic first, so he calmed everyone down and got everyone off the road," said Boon Lim, a passenger bound for Arizona.

The bus was filled with 29 passengers from all over the country, a Greyhound spokesperson said. The bus was a 2003 model and was current on its inspections.

Buck Creek Fire Chief Dave Sutherlin said it appears that a mechanical problem caused it to overheat, igniting the fire.

Some passengers were headed home and others were planning to visit relatives over the holidays.

A backup bus was brought in to transport passengers to Indianapolis. No one was injured, and the passengers' luggage was saved because crews were able to stop the blaze before it got to that compartment.