The bus was exiting I-43 just before 3 p.m. Sunday when it left the road and crashed through an embankment and ended up between warehouses, officials said.
There were 54 passengers on the bus, police said.
Green Bay Fire Department Battalion Chief Chad Bronkhorst says 33 people were transported to hospitals.
At least two injuries were reported to be critical. No deaths have been reported.
No further information was available as Wisconsin officials continue to investigate the crash.
ABC News contributed to this report.