Harrowing video has been released showing the moment a cement truck in Texas collided with a school bus packed with pre-K students returning from a trip to the zoo, killing a boy and a man.

The video, from front-facing and side-facing cameras, shows the cement truck veering across double yellow lines and crashing almost head-on with the bus, causing the bus to roll over.

Just before impact, someone can be heard crying out, and, as the bus hits the ground, a fireball appears to explode while crash debris can be seen flying around. 

The deadly incident took place at around 2 p.m. near Texas State Highway 21 and Caldwell Road in Bastrop County, a rural highway outside Austin, FOX Austin reported. 

The school bus was carrying more than 40 pre-K students from Tom Green Elementary School who were returning from a zoo field trip, many of whom were also injured.

The crash remains under investigation. Authorities have not said how fast the vehicles were traveling.

Rescuers on the scene where a cement truck plowed into a school bus packed with pre-K students last week, killing a boy and a man. (Associated Press)

No charges have been filed against the cement truck driver.

According to a report by KVUE, citing court documents, Texas police interviewed the cement truck driver while he was in the hospital for treatment on Monday, and he told them he admitted to having smoked marijuana the night before the crash.

The driver also allegedly told police that he only had slept about three hours before consuming cocaine at 1 a.m. the morning of the crash. He also refused to provide a blood sample for analysis, according to court documents.

The Associated Press contributed to this report.