A gunman reportedly killed at least 18 children at a Texas elementary school Tuesday in the deadliest shooting at a U.S. grade school since the 2012 attack at Sandy Hook Elementary School in Newtown, Connecticut.

State Sen. Roland Gutierrez said 18 children and three adults were dead, based on a briefing by state police. Three people wounded in the attack are hospitalized in serious condition, he said. CNN also reported that 18 children died.

Texas Gov. Greg Abbott and other officials said the 18-year-old shooter walked into Robb Elementary School in Uvalde around 11:30 a.m. Central time and opened fire. The shooter was likely killed by responding police, Abbott said. 

Federal law enforcement officials said the death toll was expected to rise. They spoke on condition of anonymity because they were not authorized to release investigative details.

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“This was a tragic and senseless event today, and my heart was broke today,” said Hal Harrell, the school system superintendent, who said at a news conference that grief counselors would be available and classes were canceled for the year. “We’re a small community and we’ll need your prayers to get us through this.”

Abbott said two responding officers were struck by gunfire but weren’t seriously injured.

Officials have not revealed a motive for the shooting, but have said the shooter was a resident of the community. Abbott identified the gunman as Salvador Ramos.

The gunman appeared to have acted alone, Uvalde Consolidated Independent School District Chief of Police Pete Arredondo said at a news conference.

Uvalde is a city of about 16,000 people about 85 miles west of San Antonio. The shooting came four years after a gunman fatally shot 10 people at Santa Fe High School in the Houston area.