A university building in Zurich was cleared by police Thursday after it was locked down following an anonymous threat. People inside a building in the Toni campus of the Zurich University of the Arts were told to stay indoors while the rest of the campus was evacuated, according to The Associated Press (AP).

Nearly 5,000 students were inside 1,400 rooms in the building during the lockdown, according to 20 Minuten, a local newspaper. According to Marco Cortesi, a city police spokesperson, an anonymous call forced the police to respond to the area that was cordoned off. Two ambulances were also called to the area where the situation remained calm despite police hurriedly checking the area, the report said.

Although authorities eventually sounded the all-clear, police officials said the building will remain closed for the rest of the day and that classes on campus will only resume on Friday, AP reported, adding that the investigation is still continuing at the site.

A week ago, police had responded to another alarm at the school, which later turned out to have been accidentally triggered, AP reported.