A Megabus headed from Chicago to Minneapolis caught on fire Sunday, giving its 40 passengers on board a road trip that they're not likely to forget. The fire broke out at around 12:15 p.m. local time as the Minneapolis-bound bus was headed southbound along Route 41 between Route 176 and the Lake Forest Hospital entrance, Lake Forest fire officials said, according to NBC Chicago.

First responders report coming to the scene after being notified of the incident to find the Megabus completely engulfed in flames and that all passengers and the driver were off the bus.

New Jersey-based Megabus confirmed the incident in a statement, saying, "Megabus.com can confirm that one of our vehicles traveling from Chicago, IL heading towards Minneapolis, MN was involved in an incident today near Waukegan, Ill. Safety is our top priority and Megabus.com is fully cooperating with the authorities with their investigation into the incident."

The cause of the fire is still under investigation and beyond a blown tire that preceded the flames, the only clues provided about the incident have come from passengers who appear to indicate that there were signs of problems early on in the trip, according to ABC News.

"Some people said they smelled burning," Lucas Peterson, a New York Times columnist who happened to be on board, said. "The driver kept pulling over to the side so it seemed clear there was something wrong with the bus."

He was at the scene reporting a story about Megabus which offers fares for as low as a dollar. The offering seems to be too good to be true and past instances appear to point to that being the case.

There have been at least six incidents involving blown tires on Megabuses, including one crash in 2012 that led to the death of a 25-year-old graduate student and hospitalization of 47 others, according to CBS News.

These issues have been attributed to the buses being filled beyond the capacity, which according to lawsuits, can cause the tires to rub against the wheel well, generating friction, heat and ultimately a fire. Under normal circumstances such incidents, caused by the same problem, would be rare, but the buses are only weighed before they're loaded with passengers and luggage.