Police were able to find the device and ensure it was safe, CBS said.
The suspect ran away from the scene after hurling the explosive into the restaurant on West Colorado Boulevard in Pasedena about 6 p.m., witnesses told KABC. They are still looking for the man who threw it.
Authorities could not be reached Friday morning for additional comment.
The Cheesecake Factory released a statement saying: 'This evening, an incendiary device exploded within our Pasadena restaurant.
Pasadena Mayor Terry Tornek said the device was more like a firecracker than a bomb.
"They'll investigate this thoroughly, because it was a disruptive thing", he said. Still, he said police are taking the incident seriously, according to the Star-News.
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Witnesses described the suspect as about 6 feet tall, with a thin build and heavy beard, according to police.
"Thankfully, none of our guests or staff was injured", Alethea Rowe, senior director of public relations for The Cheesecake Factory Incorporated, said in a statement Thursday night.
The man was wearing all black clothing and a black beanie, according to the Police Department.
The restaurant is in the historic Old Pasadena dining and shopping district. "That intersection is travelled heavily by our officers", Goodman said.
Anyone with information was asked to call the Police Department at 626-744-4241. Tips may also be submitted anonymously to L.A. Regional Crime Stoppers at 800-222-8477.