Videos surface of desperate parents begging police to storm Robb Elementary School, where a teenage gunman killed 19 small children and two teachers two days ago before being shot dead by officers "approximately an hour" later.

"There was at least 40 lawmen armed to the teeth but didn't do a darn thing (until) it was far too late," father of a victim says. (Reuters)

Texas police have faced angry questions over why it took an hour to neutralise the teenage gunman who murdered 19 small children and two teachers in Uvalde, as video emerged of desperate parents begging officers to storm the American school.

In one jolty, nearly seven-minute clip posted on YouTube, parents living a nightmare — a school shooting under way with their kids inside — are seen screaming expletives at police trying to keep them away from Robb Elementary School.

"It's my daughter!" one woman bellows amid chaotic scenes of crying and shoving.

Angeli Rose Gomez, whose children were inside, told The Wall Street Journal she was handcuffed by federal marshals after she and others pushed police to intervene.

In another shorter video, parents at what is apparently the rear of the building complain angrily that police are doing nothing as the country's worst school shooting in a decade is unfolding.

One woman, frantic about her son, yells to police, "if they've got a shot, shoot him or something. Go on."

Jacinto Cazares, whose daughter Jacklyn died on Tuesday, said he raced to the school when he heard about the shooting.

"There was at least 40 lawmen armed to the teeth but didn't do a darn thing (until) it was far too late," Cazares told ABC News on Wednesday.

"The situation could've been over quick if they had better tactical training."

Daniel Myers and his wife Matilda — both local pastors —  told the AFP news agency they saw parents at the scene growing frantic as police seemed to wait on reinforcements before entering the school.

"Parents were desperate," said Daniel Myers, 72. "One family member, he says: 'I was in the military, just give me a gun, I'll go in. I'm not going to hesitate. I'll go in.'"

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'Approximately an hour'

The tight-knit Latino community was changed forever when Salvador Ramos, an 18-year-old with a history of being bullied, entered the school and gunned down students and teachers with an assault rifle.

Relatives said the husband of one of the teachers killed died on Thursday from a medical emergency — caused by grief over the loss of his wife. The couple had four children.

Facing rapid-fire questioning by journalists on the police response, Victor Escalon of the Texas Department of Public Safety (DPS) said investigators were still working to piece together exactly what happened.

After shooting his own grandmother, Escalon said Ramos crashed her vehicle near the school, fired on bystanders, then entered through a door that was apparently unlocked.

Officers went in minutes later, but were held back by gunfire and called for backup. A tactical team including US Border Patrol agents entered and killed the gunman "approximately an hour later."

In the interim, officers evacuated students and teachers and unsuccessfully tried to negotiate with the gunman, who held them back with rifle fire, Escalon said.

He also refuted earlier accounts that the gunman was confronted by a school resource officer, and said there was no armed officer on site when the attack began.

Uvalde's police chief, Daniel Rodriguez, also addressed the controversy over the response time, saying: "Officers responded within minutes."

"I understand questions are surfacing regarding the details of what occurred. I know the answers will not come fast enough during this trying time," Rodriguez said in a statement.

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Source: AFP