Three people were take to Jefferson Memorial Hospital in Ranson, W.Va., but were expected to be taken back to the track later, fire and track officials said.
It was believed a brake stuck, causing a back tire to skid along the road and catch fire, Smith said
The fire was called in at 5:53 p.m., Smith said. When he arrived at the entrance to the track along East Washington Street, the fire was in the rear of the bus, Smith said.
It took less than a minute for the blaze to spread to the front of the bus, Smith said.
All the passengers were off the bus by that time, Smith said.
Passengers in the rear section of the bus said they could feel the heat and one passenger said she was trying to move to the front of the bus but people at the front were not moving fast enough.
"I'm 80 years old and I had to jump out the back window," said passenger Mary Wierman of Hanover, Pa.
Wierman said the flames were starting to lap around her legs while she was at her seat.
Wierman said another woman opened the window for her and a man outside helped her make it through the window.
"I just fell on my arm. We had a good angel or something looking over us. I could have been blown up," said Wierman as she sat with other passengers in a grassy area away from the fire.
Amelia Prisco, who said she was sitting in the back of the bus, said she helped a woman out one of the windows. Prisco said she then tried to climb out, but flames were reaching up around the window.
"I thought, 'My God, I'll burn to death like this,'" said Prisco, of Baltimore.
Instead of climbing out, Prisco said she "just kept pushing" until she reached the front of the bus.
The bus stopped just inside the entrance to the track. After the fire was extinguished, onlookers gazed at the burned-out body of the bus.
Some of the wheels were burned off and windows were broken.
The fire severed a diesel fuel line on the bus, causing about 125 gallons of fuel to run down Washington Street, Smith said.
Volunteer firefighters did an excellent job containing the fuel by using a water hose to catch it before it escaped, said Berkeley County Office of Emergency Services Director Steve Allen.
Allen was called to the scene as part of a hazardous materials team.
Smith said he heard some explosions shortly after he arrived and assumed they were tires exploding. The tire that initially caught fire was laying on a grassy area near the bus.
Smith said the tire may have exploded, come off the bus and landed in the grass.
The bus passengers, who were on their way to Charles Town Races & Slots from Hanover, were taken to the track and provided with drinks or whatever they needed, said David L. Whitley, the track's vice president of compliance.
Another bus was expected to be sent to the track from Hanover to pick up the passengers, Whitley said.
The bus was operated by Lincoln Bus Lines, which is located in the Hanover area, Whitley said.
The driver of the bus declined to comment. Officials would not release the driver's name.