One person was killed and dozens were injured after a tour bus carrying about 50 passengers overturned on a Delaware highway on Sunday, authorities said. According to reports, about five of the injured people are in critical condition.

The accident reportedly took place near Red Lion Road off Route 1 in the community of Bear, about 12 miles south of Wilmington, the state's largest city. Officials reportedly said that the cause of the accident was unclear and that an investigation is underway. A Delaware State Police spokesman said that, based on preliminary information, it did not appear that any other vehicle was involved in the crash. About 49 people had been reportedly taken to local hospitals for treatment.

"We're still investigating the cause of this crash. We're interviewing passengers and the driver to see what exactly happened," Sgt. Paul G. Shavack said, according to Los Angeles Times.

Shavack also reportedly said that at least two Delaware State Police helicopters and one Maryland State Police helicopter airlifted some of the critically injured passengers to nearby hospitals.

Authorities reportedly said that the woman who died in the accident was ejected from the bus before being trapped under the vehicle.

"I guess she was trapped underneath the bus," Elvis D'cruz, a 19-year-old college student from New Castle, Delaware said, according to NBC 10. "One man was saying, 'my wife, my wife, my life.' That keeps replaying in my mind.

"It must've been within five minutes of the crash," D'cruz reportedly said. "There were about two to three other civilians there helping out. The bus had flipped over onto its side and some people were still underneath it.”

Officials reportedly said that it was unclear where the single-deck tour bus was headed and from where the trip began.

"We are interviewing the driver to try and determine what happened and where it was going," Shavack said, according to Reuters.