Local authorities say an alert about a possible gunman at a school in western Germany was a false alarm.

Officers were sent to the school in Menden after receiving an alert from inside, reportedly from a portable alarm.

"The report of an attack in Menden was a false alarm," the authorities for Arnsberg district said in a message on Twitter.

"Thanks to all of the emergency responders who reacted so quickly."

They also tweeted the message in English:

We can confirm that this was a false alarm. Thx to all police and medical forces! #Menden

— BezReg Arnsberg (@BezRegArnsberg) February 22, 2017

A spokesman for Menden police said officers had found no evidence of an attacker or any injured persons.

Students at the school were reportedly told to lock themselves inside their classrooms during the alert.