The two-alarm blaze was reported at about 9:20 p.m. at Zheng Long Pan-Asian Bistro, 1448 S. Main St., across the street from Kaiser Permanente Walnut Creek Medical Center.
The restaurant was closed at the time of the fire and had been undergoing extensive remodeling during the past three weeks, fire district spokeswoman Emily Hopkins said.
An investigation indicated that the fire originated on the rear deck of the restaurant and was caused by materials used for the renovation, Hopkins said.
The fire then spread to the restaurant before it was brought under control at about 10:30 p.m., according to Hopkins.
