The gunman who killed at least 19 children and two adults at Robb Elementary School in Uvalde, Texas, on Tuesday has been named as 18-year-old Salvador Ramos, reports The Independent and agencies.

Governor Greg Abbott said Ramos "horrifically and incomprehensibly" carried out the mass shooting alone before being shot dead by law enforcement officers.

Ramos was a student at Uvalde High School who lived in the small city 80 miles west of San Antonio, according to Mr Abbott.

Ramos had hinted on social media that an attack could be coming, state Sen Roland Gutierrez, who was briefed by police, told reporters. "He suggested the kids should watch out," the lawmaker said.

He shot his grandmother before driving to Robb Elementary just before midday on Tuesday, Mr Abbott said at a news briefing on Tuesday afternoon. She is in a critical condition, Texas Department of Public Safety Sgt Erick Estrada told CNN.

Ramos is believed to have abandoned his car outside the school and entered the school grounds with a handgun and possibly a rifle. Police said the killer was wearing body armour.

"The suspect made entry into the school and as soon as he made entry into the school he started shooting children, teachers, whoever’s in his way," Christopher Olivarez of the Texas Department of Public Safety told local media.

Officers responding to the scene reportedly shot Ramos dead. Roland Gutierrez, a state senator who was briefed by the Texas Rangers said that Ramos had purchased the guns on his 18th birthday.

"That was the first thing he did on his 18th birthday," he said.

Uvalde Memorial Hospital initially said 13 students and an adult were transported from the school by a bus and ambulance. Two of the students were pronounced dead on arrival. But the death toll rose steadily risen, with officials revising it from 14 to 19 students and two adult victims by Tuesday evening.