The Mansfield Independent School District said in a news release that the school was on lockdown Wednesday morning.
The “unknown suspect” immediately fled the scene after opening fire, according to that preliminary briefing. The number of victims and their conditions is unknown.
Police said the scene at the high school is currently secure, and there is no current threat to the public or the school.
The police department said on Twitter that officers were doing a “methodical search” and were working closely with other law enforcement agencies.