Chicago, Aug 4 (IANS): A 25-year-old woman dentist from Mumbai, who was also a graduate student at the University of Missouri, was the lone passenger killed in a crash of a double-decker bus in Illinois.

Aditi R. Avhad, was headed from Chicago to Columbia, Montana Thursday when the bus slammed into a highway overpass support pillar near Litchfield, about 55 miles northeast of St. Louis, Chicago Tribune reported.

As many as half of the passengers were injured, the daily said citing State Police Capt. Scott Compton. Four to five of them were trapped and had to be extricated, including Avhad.

Avhad, a dentist from Mumbai, was enrolled in the graduate programme at the University of Missouri's School of Medicine, according to the school. She was studying for a master's degree in health administration and hoped to get her degree next year, officials said.

She was riding in the upper deck with her parents when the bus crashed, police said. Passengers said the impact sent them flying from their seats.

The state police cited by the Tribune said preliminary reports showed at least 33 people were taken to area hospitals.

Police believe the bus blew a tire but are still looking at circumstances of the accident. That investigation could take weeks, they said.