PASSAIC, N.J.—A fire near a New Jersey chemical plant with flames and smoke visible for miles in the night sky spread to multiple buildings in the complex Friday, threatening to reach the plant’s chemical storage area, authorities said. Passaic Mayor Hector Lora told residents in a video posted on Facebook to stay away from the area and keep their windows closed. Lora said firefighters were still assessing the situation. There were no initial reports of loss of life, he said. Passaic Fire Chief Patrick Trentacost said the building was vacant when the fire broke out. “A portion of the building did have chlorine in it and that seems to be under control at this time,” he said just after midnight. “We’ll be monitoring that also throughout the night but certainly we’re far from having control of the fire.” The fire chief also said much of the building where the fire …