German police escorted students out of a school in the northern city of Hamburg on Wednesday, acting on information that two youths had entered a classroom and brandished something that resembled a gun, they said.

Police took four children, aged 12 to 14, into temporary custody. They later concluded that two of them were behind the incident, which had involved a toy gun.

The other children were taken to a nearby military barracks where they waited for their parents to pick them up. Investigations are ongoing, police said.

Pupils and teachers had been asked to lock themselves in their classrooms in the late morning, TV channel ARD said, but police did not immediately confirm this.

Hamburg was recently the scene of an hostage standoff at the airport that had forced authorities to close the busy hub for hours.