LAKE FOREST, Ill. (AP) — Fire officials in suburban Chicago said Monday that they're investigating the cause of a blaze that struck a Minneapolis-bound Megabus.

None of the 40 passengers aboard the bus Sunday afternoon were injured, the Lake Forest Fire Department said. Deputy Chief Pete Siebert said Monday morning that the department was "actively investigating the cause of the fire" and didn't immediately have more details about the cause.

Firefighters used water and firefighting foam to put out the blaze along Route 41 near Waukegan and the Lake Forest Hospital. Afterward media photos showed the bus was charred, with broken out windows and peeled paint.

Passengers said the driver pulled over after hearing a loud pop and seeing smoke coming from a tire.

"We checked the smoke and started walking a little bit away and then maybe 30 seconds later after we all got back about 50 feet, we heard a loud boom, big explosion, and the bus went on fire, smoke maybe 30 feet in the air," passenger Alec Grych told WLS-TV in Chicago.

Many passengers said they lost all of their luggage and belongings in the fire. They also praised the bus driver for trying to salvage their belongings despite the blaze.

"He was trying to risk his own life to throw our luggage out, but he couldn't because the smoke was too dangerous," passenger Russicha Watkins said. "Fire came from everywhere."

Sean Hughes, director of corporate affairs for the line's parent company, Coach USA North America, said it was "fully cooperating" with the investigation and that safety is priority.

The incident is the latest of several for Megabus in Illinois and Indiana. Megabus had four crashes in Indiana between October 2014 and April 2015. Charges were filed last May in Illinois against a man who authorities said fired a gun on a Minneapolis-bound Megabus shortly after it left Chicago.