CHARLESTON TOWNSHIP, Mich. -- Authorities say an American woman who was critically injured Thursday when a Greyhound bus travelling from Toronto to Chicago crashed in southwestern Michigan is showing improvement.

In all, authorities say 22 people -- including the driver -- were hurt when the bus hit the back of a semi-truck on westbound Interstate 94 in Kalamazoo County's Charleston Township.

Most of the injuries were described as minor.

The Kalamazoo County Sheriff's department says 65-year-old Cecillia Cheng of Darien, Ill., was listed in stable condition Friday after being in critical condition earlier.

It says she was a front-seat passenger on the bus.

Greyhound Canada says it can't confirm how many Canadians were on board.

The company said Friday the cause of the crash is under investigation and it's not yet known how badly the bus was damaged.

It's unclear how many people were on the bus, with authorities saying 48 passengers and Greyhound saying 36.

A Kalamazoo Metro Transit bus picked up the stranded passengers and took them to a transportation centre in downtown Kalamazoo, where they boarded another bus to Chicago.

"I woke up just saw glass shattering everywhere all over me," Marissa Desimone of the Toronto area told a local Michigan TV station, Wood TV 8.

Desemone, who was headed with friends to the Lollapalooza concert that starts Friday in Chicago, was sitting directly behind the bus driver. She told the TV station that her head slammed into the glass in front of her and the woman next to her was thrown from her seat.

With files from The Associated Press