(CNN) -- A school bus wreck killed a young child on the bus and the bus driver Monday in Indianapolis, officials said. Ten other children were injured, including two critically, according to the Indianapolis Fire Department. The girl killed in the wreck was estimated to be 5 or 6 years old. The wreck happened just before 8 a.m. on Emerson Avenue in southeastern Indianapolis, the fire department said. An investigation into the cause of the accident is under way. Witnesses said they saw nothing unusual before the bus hit an abutment beneath a concrete overpass, according to fire department spokeswoman Rita Burris. Officials are waiting for a coroner's report to determine if the driver had a medical condition that could have contributed to the wreck. CNN's Deanna Proeller contributed to this report.
Ten other children are injured, two critically, fire department says . Witnesses report nothing unsual before the bus wreck in Indianapolis . An investigation is under way .