Maryland police are investigating what led to a bus filled with middle school students driving off the road and overturning in Columbia on Thursday afternoon, resulting in several occupants being evaluated for injuries.

Photos of the single-vehicle crash show a full-size school bus in the grass next to a two-lane road, with roof hatches opened and EMS crews tending to people outside the bus.

The Howard County Police Department said the bus flipped over in the 7300 block of Old Columbia Road in Columbia just after 3:30 p.m.

There were 19 students from Hammond Middle School onboard when the bus crashed.

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Police said of the 19 students, two boys and two girls between the ages of 11 and 14, were transported to a nearby hospital to be evaluated for injuries.

The driver of the bus, a 30-year-old woman, was not injured in the crash. Police also said there were no indications that the driver was impaired.

Police have not disclosed why the bus swerved off the roadway and into the grass, as the investigation into the incident is ongoing.

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Howard County school officials did not immediately respond to inquiries from Fox News Digital about the crash.

Shortly after the incident, Howard County Public School officials sent a message to families of students in the district to alert them to what happened, according to FOX 5 in Washington, D.C.

"This afternoon there was a significant bus accident with Hammond Middle School students on board," the announcement read, adding that several students were injured and receiving medical care.

The station also reported that the students who were not harmed were sent home with their families.