The father of Amerie Jo Garza, one of the children killed in the mass shootout at a Texas school weeks after her 10th birthday, said he learned of his daughter’s death while giving her best friend medical aid.

Texas’s Robb Elementary School in Uvalde on Tuesday became the site of the deadliest shooting in the US in a decade after an 18-year-old gunman killed 21 people, including 19 children and two adults.

Angel Garza, a medication aide, said he arrived at the scene as one of the first responders to help rescue operations when he found out about his daughter’s death from her best friend.

Speaking to CNN’s Anderson Cooper, Mr Garza said he saw one little girl who was “just covered in blood” from “head to toe”.

“She was hysterical saying that they shot her best friend, they killed her best friend, that she’s not breathing,” he said.

“That she was trying to call the cops. And I asked the little girl the name and she said Amerie,” he added.

“She was so sweet. She was the sweetest little girl who did nothing wrong.”

Police have confirmed that all 21 victims were in Amerie Jo’s classroom. The shooter, identified as Salvador Ramos, had used a handgun and rifle in the attack and was subsequently shot dead by police.

Amerie Jo’s grandmother had earlier said the little girl had tried to call 911 for help when the shooter entered the classroom.

“So the gunman went in and he told the children, ‘you’re going to die.’ And [Amerie] had her phone and she called 911. And instead of grabbing it and breaking it or taking it from her, he shot her. She was sitting right next to her best friend. Her best friend was covered in blood,” her grandmother Berlinda Irene Arreola was quoted as saying to The Daily Beast.

Two other students in the classroom confirmed Amerie had attempted to call for help, reported Insider.

Mr Garza said Amerie had received her phone just weeks ago on her 10th birthday.

“She’d been wanting a phone for so long and we finally got it for her,” he said.

“She was trying to do the right thing. She was just trying to call the cops... and I guess he just shot her.”

He said he wanted people to know his daughter had died trying to save people.

“How do you look at this little girl and shoot her?” he said. “How do you shoot my baby?”