Disturbing new footage has emerged from the Texas shooting incident showing panic-stricken students trying to escape from the gunman through a broken window.

The video surfaced days after 18-year-old Salvador Ramos opened fire at Robb Elementary School in Uvalde, Texas. Ramos killed 19 children and two teachers who were holed up inside a classroom in the school on that fateful day.

Ramos had shot his grandmother in the face before driving off in a pick-up truck to the school and going on a killing spree. His grandmother is undergoing treatment at a hospital and is still in critical condition.

The new video from the day of the incident has been released by Good Morning America, and shows the chaos while students were trying to somehow run to safety. Dozens of police officers could also be seen surrounding the building when a window suddenly gets smashed by someone from inside.

The officers can then be seen lifting the students out of the window and directing them to run away from the school. Another video shows a group of students coming out of a back door and running away as fast as possible.

Meanwhile, the first responders have come under severe criticism for failing to respond quickly in the situation. According to local media reports, the officers in Uvalde took more than an hour to confront the shooter which is a significant amount of crucial time.

The US Department of Justice has now decided to carry out a review of the law enforcement officers' response to the shooting at Robb Elementary School on May 24, per a report in The Independent.

"The goal of the review is to provide an independent account of law enforcement actions and responses that day, and to identify lessons learned and best practices to help first responders prepare for and respond to active shooter events, "said Justice Department spokesman Anthony Coley.

The Texas incident is one of the deadliest school shootings in the United States since the 2012 attack in Newtown, Connecticut. The mass casualty shooting is the latest in the United States, where firearms are involved in approximately 40,000 deaths a year, including suicides, according to the Gun Violence Archive website.

Lax gun laws and a constitutionally guaranteed right to bear arms have repeatedly stymied attempts to clamp down on the number of weapons in circulation, despite greater controls being favoured by the majority of Americans.

Two teachers and 19 students were killed in a shooting at Robb Elementary in Uvalde, Texas. Reuters / Pete Luna/Uvalde Leader-News