WAUKEGAN, Ill. (AP) - A large explosion has blown the top off a shopping plaza in Waukegan, Ill. Police say at least six people have been taken to a hospital.

The explosion struck around lunchtime Thursday. It blew the windows out of storefronts and collapsed the ceilings above stores.

Witness Candi Rixie was taking orders at a sandwich shop a block away. She said she felt a rumble, almost like somebody hit the building with a car.

It wasn't immediately clear what caused the blast, but crews from People's Gas were on the scene to investigate.

Fire crews from several towns have come to help in rescue efforts, and are searching to see if people are trapped inside.