An off-duty Chicago police officer was killed after police chase that started in a south suburb ended in a crash just off the Dan Ryan Expressway on the South Side early Friday, police said.

About 1 a.m., police in south suburban Calumet Park chased a vehicle onto the Dan Ryan expressway early Friday, police said. The chase ended about 1 a.m. with a crash in the 8700 block of South Lafayette Avenue, just off the Dan Ryan.

The officer’s age, gender and rank were not immediately known. The Cook County Medical Examiner’s office could not confirm the death Friday morning.

It was not known what prompted the chase onto the Dan Ryan, and Calumet Park police declined to comment.

The Chicago police Major Accidents Investigations Unit was investigating the crash.