Nineteen young children and two adults have died in a shooting at a primary school in south Texas.
The 18-year-old gunman opened fire at Robb Elementary School in the city of Uvalde before he was killed by law enforcement, officials said.
Investigators say the suspect was armed with a handgun, an AR-15 semi-automatic rifle and high-capacity magazines.
The teenager is suspected of shooting his grandmother at the start of the rampage.
Local media report he may have been a high school student in the area.
Uvalde Consolidated Independent School District Chief of Police Pete Arredondo said the shooting began at 11:32 local time on Tuesday, and that investigators believe the attacker “did act alone during this heinous crime”.
Texas Governor Greg Abbott said the shooter, whom he named as Salvador Ramos, abandoned a vehicle before entering the school to “horrifically, incomprehensibly” open fire.
One of the adults killed was a teacher, who has been named in US media as Eva Mireles. Her page on the school district’s website said she has a daughter in college and loved running and hiking.
Just under 500 pupils are enrolled in the predominantly Hispanic school around 85 miles (135km) west of the city of San Antonio.
Robb Elementary teaches second, third and fourth grade students, who range in age from seven to 10 years old.
The Associated Press news agency reports that a US Border Patrol official who was nearby when the shooting began rushed into the school and shot and killed the gunman, who was behind a barricade.
Border Patrol is a federal agency that guards US ports of entry. Uvalde, which is fewer than 80 miles from the border with Mexico, is home to a Border Patrol station.
Two border agents were reportedly shot in an exchange with the gunman. One agent was shot in the head, officials say, adding that both were now in a stable condition in hospital.
According to CBS News, the attacker was wearing body armour as he carried out the attack. Another 18-year-old who is suspected of attacking a grocery store in Buffalo, New York, on May 14 was also wearing body armour and carrying a semi-automatic rifle – both of which are commercially available in the US.
The Uvalde Memorial Hospital posted on Facebook earlier that 13 children had been taken to hospital “via ambulances or buses”.
A 66-year-old woman and a 10-year-old girl were in a critical condition at a hospital in San Antonio, University Health hospital officials say.
Just a few blocks from the Robb Elementary school, a small vigil was held for the victims and survivors of the attack. (BBC)