Authorities were called after a white powder was found Thursday morning at a CTA Red Line station in the Loop.

The “unknown white substance” was found at 9:24 a.m. on the mezzanine floor of the Lake Street station, 188 N. State St., according to Chicago Police and the CTA.

The station was closed and trains bypassed it while authorities investigated the powdery substance, a CTA spokesman said. It was reopened by about 9:45 a.m. after investigators determined that there was no danger.

Further details were not immediately available.