Timeline of how Texas school shooting unfolded

The mass shooting at Robb elementary school in the small city of Uvalde, south Texas, began on Tuesday 24 May with a single shot.

An 18-year-old local man, who just a few weeks before had reached the age where he could legally buy a military-style assault rifle, sent ominous social media messages pre-dawn, including telling someone he was going to shoot his grandmother.

He seemed panicked and struggled to get the Ford going, the neighbor, Gilbert Gallegos, said, then drove off in a spray of gravel.

Moments later, the grandmother, Celia Martinez Gonzales, 66, who is known as Sally, came out covered in blood after being shot in the face, crying out. She has survived and remained in the hospital on Monday.

By 11.28am the gunman had reached Robb elementary, half a mile away, and crashed the pickup in a ditch, authorities said.

At that moment, video shows a teacher entering the school through a door that the teacher had emerged from and propped open moments earlier.

That door was usually closed and locked, according to the school security protocol, but was ajar.

The gunman had an assault rifle and a backpack crammed with ammunition, and shot at two men who emerged from the funeral home right across the street from the school.

But the officer initially headed for the wrong man, confronting someone who turned out to be a teacher, after passing Ramos, who crouched behind a vehicle.

The gunman slipped through the open door and into adjoining fourth-grade classrooms packed with nine, 10 and 11-year-olds, overseen by two teachers, at 11.33am, authorities said.

The Associated Press chronicled the incident based on law enforcement reports, records and interviews with Uvalde residents.

The shooter rapidly fired more than 100 rounds then moved into the adjacent room, where witnesses heard screams, more gunfire and morbid music being blared by Ramos.

Two minutes after he entered the school, three police officers followed and were quickly joined by four more.

In the nearly half-hour after the first officers went inside, as many as 19 piled into the hallway, authorities said.

Meanwhile, children and teachers elsewhere in the building were trying to escape, some climbing out of windows.

He saw about five officers helping people evacuate and about 20 minutes after arriving said he spotted officers coming with heavy shields for the first time.

At 12.03pm, a girl called 911 and whispered that she was inside the classroom with the gunman.

The girl called 911 twice more, talking of multiple dead but also children still alive. There was sporadic gunfire, the authorities have said.

Cazares and relatives later spent three desperate hours at a hospital before being told Jacklyn, 10, had died.