Police ordered a shopping mall in the western German city of Essen not to open Saturday after receiving credible tips of an imminent attack.

The shopping center and the adjacent parking lot stayed closed as about a hundred police officers positioned themselves around the compound to make sure nobody could enter the mall. Several officers scoured the inside of the building to bring out early morning cleaning staff.

"As police, we are the security authority here and have decided to close the mall," police spokesman Christoph Wickhorst said, adding that they had been tipped off late Friday by other security agencies. He did not want to provide further details because of the ongoing investigation.

The downtown mall at Limbecker Platz square will be closed for the entire day. The mall is one of the biggest in Germany with more than 200 stores, according to the shopping center's website.

In 2016, three people were injured in an attack on a Sikh temple in Essen by radicalized German-born Muslim teenagers.

Germany has been on the edge following a series of attacks in public places over the past year.

Most recently, a mentally disturbed man attacked travelers with an ax at the central train station in the west German city of Dusseldorf Thursday, injuring seven people before he was captured.

Ax attacks are not unheard of in Germany. Last July, a 17-year-old Afghan refugee injured five people on a regional train in the central town of Wurzburg before he was killed by police. The refugee later claimed in a video to be acting on behalf of ISIS.