Oslo — Norwegian police swarmed a secondary school in the southeastern town of Fredrikstad on Thursday and arrested a person who made threats against the building, police said after evacuating the school.

"The situation appears to be clarified. A person has been arrested," police said in a statement.

Police had earlier announced the evacuation of the Glemmen secondary school in Fredrikstad after someone threatened to use "serious violence" against it.

The exact nature of the threat and the way it was presented were not disclosed.

According to Norwegian media, the person arrested is a teenager who posted a menacing message online as a prank.

The online edition of the local newspaper Fredrikstad Blad reported that some 1,000 students and 100 to 200 teachers were evacuated from the building.

Police were immediately rushed to the scene.

Pictures published on the newspaper’s website showed the school being swarmed by armed police officers wearing bullet-proof vests. It was to remain closed Friday, police said.

The scare came just a few weeks after a school shooting in the German town of Winnenden, where a teenager massacred nine students, three teachers and three passers-by on March 11.

AFP/Expatica