NORTHLAKE, Ill. (CBS) — Two people were killed early Thursday when a semi-trailer truck collided with five other vehicles on the Tri-State Tollway in the north suburbs.

Illinois State Police spokeswoman Monique Bond said, according to preliminary reports, a truck rear-ended a car on I-294 near Lake Street sometime between 5:45 a.m. and 6 a.m. on Thursday. The collision caused a chain reaction, involving four more vehicles.

Two people were killed in the crash, Bond said. Their identities were not being released Thursday afternoon.

The cause of the crash was under investigation.