Two people died in the school shooting, and 13 children were being treated for various injuries at Uvalde Memorial Hospital, spokesperson Tom Nordwick said. A man in his 40s was also being treated, he said.
Two children were transported to San Antonio and another is pending transfer, he added.
Videos taken by a bystander, Isaias Melendez, show scores of armed officers at the scene while others flee the school.
The school district said it is canceling all school activities following the shooting.
The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are assisting local police with the investigation.
This is a developing story and will be updated.