A 31-year-old woman was sexually assaulted Wednesday evening after being knocked unconscious as she walked in the Rogers Park neighborhood on the North Side, police said.

The woman was walking south about 6:40 p.m. in the 6600 block of North Clark when a male grabbed her from behind and put his wet hand over her nose and mouth, according to a community alert from Chicago police. The man, whose hand smelled similar to alcohol, proceeded to pull the woman backward before she lost consciousness.

The woman later woke up alone in an unfamiliar building after being sexually assaulted, police said. The suspect then ran off.

No one is in custody, police said.

Anyone with information about the attack should call Area North detectives at (773) 744-8261.