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WENTZVILLE  • Holt High School was on lockdown for a few hours Tuesday morning after a "very vague threat" on social media, police said.

The social media message said students should leave the school because "the halls are gonna be a mess at 9:20," district spokeswoman Mary K. LaPak said.

A student alerted the school's resource officer about the message. Police and school administrators locked down the school about 9 a.m. as a precaution. Police swept the school and spoke to students involved in the social media thread before determining there was no credible threat, LaPak said. The district announced on its website late Tuesday morning that the lockdown had been lifted.

The high school is at 600 Campus Drive, a half-mile north of Interstate 70.

Meanwhile, in O'Fallon, Mo., on Tuesday, police and school officials investigated an incident at Frontier Middle School and determined it "was not credible," said O'Fallon Police Officer Diana Damke. She did not elaborate on what led to the police investigation. 

Frontier Middle School, at 9233 Highway DD in O'Fallon, is also in the Wentzville School District.

On May 9, a school resource officer played a key role uncovering an incident at Wentzville Middle School, at 405 Campus Drive. The student brought an unloaded gun onto school property morning but was stopped by a school resource officer before he got inside.

Kim Bell is a reporter for the St. Louis Post-Dispatch.