An unknown man set off an explosion at a Pasadena Cheesecake Factory in California that sent customers ducking and running for cover.

Witnesses said the suspect opened the door of the crowded restaurant around 6pm on Thursday and lit and threw the homemade device before fleeing towards Fair Oaks Ave.

The explosive was said to have landed at on unoccupied table and which gave off heavy smoke, NBC Los Angeles reported.

The popular restaurant chain located on the corner of Fair Oaks Avenue and East Colorado Boulevard in Pasadena was evacuated after an unknown man threw an explosive device

'People were jumping over one another, fighting to get over bar stools. People were tripping, falling...stuff going everywhere. It was very chaotic,' said one witness, Garrett Gunkle, who returned to the restaurant to collect his belongings.

Unfinished plates of food and personal belongings were abandoned mid-meal.

Los Angeles County Sheriff's Department bomb squad arrived at the restaurant and found the 'pyrotechnic device' containing gunpowder.

Restaurant patrons abandoned their unfinished meals and fled after the device exploded and set off a heavy smoke

No customers were hurt in the incident and the motive is still unknown police said. The suspect was described by witnesses as a 'Hispanic or Middle Eastern' man with a thin build and a beard.

The Cheesecake Factory released a statement saying: 'This evening, an incendiary device exploded within our Pasadena restaurant.

'Thankfully, none of our guests or staff was injured. Law enforcement is actively investigating the incident, and we hope to reopen in Pasadena on Friday, as usual.'