An unknown assailant hit a Wrigleyville woman in the head and then sexually assaulted her as she was entering her apartment building early yesterday morning.

The incident happened at 4:30 a.m. on the 3700 block of N. Lakewood Ave., police said.

Detectives have issued a community alert and are urging people to beware of any suspicious activity.

Anyone with information regarding this incident is encouraged to call Area 3 Detectives at (312) 744-8261.