Seven people were killed and dozens more injured when a passenger bus bound for Mexico suffered a tire failure and overturned east of Vicksburg, Mississippi, officials said today.

Among the victims were siblings who were 6 and 16, Warren County Coroner Doug Huskey said.

The National Transportation Safety Board, which is leading the investigation, will consider several factors during its review, including the safety of the motor carrier and tire maintenance, NTSB member Todd Inman said at a news conference.

Thirty-seven passengers were transported to hospitals in Vicksburg and Jackson with unknown injuries, the Mississippi Highway Patrol said.

"Anytime you have people injured or dead, it's tragic, but when you have a situation like this where you have multiple casualties and injuries, it makes it even worse," Warren County Sheriff Martin Pace told WAPT. CNN affiliate.

The bus belongs to Autobuses Regiomontanos, which transports passengers between Mexico and the United States, according to Miranda Fernandez, a spokeswoman for the company.

The company is based in Monterrey, Mexico, Fernandez said, and has several locations in the United States, according to a company website. It's unclear which city the bus originated in, according to Fernandez, but it was en route to Mexico.

"All passengers go through the appropriate immigration checkpoints and must show their passports or visas to enter Mexico or the United States," Fernandez told CNN.

"Several Mexican identification documents" were found on the bus, according to Mississippi Highway Patrol spokesman Kervin Stewart.

Six passengers were pronounced dead at the scene, and a seventh died at a hospital, according to the highway patrol.