German police said on Wednesday that they had deployed forces to a school in the town of Menden near Dortmund, where a media report said there was an armed man.
The college, which has about 2,000 students and 100 teachers, went into lockdown at around 11.15am local time, after pupils and staff were told to lock classroom doors.
The press office of the district government Arnsberg later said that the alert was a false alarm after no gunman could be found.
‘Thank you to all forces who quickly responded,’ the government agency said in a tweet announcing that it had been a false alarm.
A police spokesman told broadcaster n-tv during the ongoing operation in Menden and that no one had been injured.
People were instructed to stay inside at a nearby nursery school as well, according to local reports.
Helicopters were seen circling the area, and armed police and ambulances were on the ground.