Investigators are looking into the cause of a fire that broke out Thursday morning on the Upper West Side of Manhattan.

It started just before 10 a.m. in duct work in the back of Ollie's restaurant at 1991 Broadway, a few blocks north of Lincoln Center.

The fire spread up through two floors before it was brought under control just before 10:30 a.m.

"If you don't clean out the grease in the ducts, what happens a lot of times is that grease builds up. So, a small flame will start, work its way up that grease, and then it works its way up the two stories and out the top from the grease burning," said FDNY Battalion Chief Mike Myers.

Of the more than 60 firefighters responded to help put out the flames, two sustained minor injuries.