A child was killed Wednesday after a sedan plunged off Interstate 10 East near the San Jacinto River, authorities said.

The sedan and an 18-wheeler were both westbound on the East Freeway near Crosby-Lynchburg around 7 a.m. when the big rig changed lanes and hit the car, according to Harris County Sheriff's Office Sgt. Eduardo Rivera. The sedan was pushed up over the left concrete barrier that protects cars from falling off the bridge, Rivera said.

Now Playing:

The car somehow fit between that barrier and another one on the eastbound side of the bridge, falling to the dry riverbed below, Rivera said.

The child was not properly restrained, according to Harris County Sheriff Ed Gonzalez.

A 4-year-old girl was found dead underneath the crumpled sedan, while her 35-year-old father had to be pried free by firefighters, authorities said. He was airlifted to a Houston hospital in critical condition.

The girl's 24-year-old mother was also in the car and suffered only minor injuries, Rivera said. She was shaken up but was treated by paramedics on scene and released soon after.

The driver of the big rig is cooperating with investigators as they work to determine what happened – particularly if he broke any laws that caused the crash. As of 10 a.m., he was not facing any charges, Rivera said.

The crash closed several westbound and eastbound lanes of the freeway as investigators worked.

Jay R. Jordan covers breaking news in the Houston area. Read him on our breaking news site, Chron.com, and our subscriber site, HoustonChronicle.com | Follow him on Twitter at @JayRJordan | Email him at jay.jordan@chron.com | Text CHRON to 77453 to receive breaking news alerts by text message