The site is near the intersection of Larkfield and Clay Pitts Road. Police and fire officials were notified of the incident just before 1 p.m., officials said. It remained closed after 6 p.m.
Police said National Grid has been notified.
The road is closed between Clay Pitts and Meadow Lark Drive.
The construction project is believed to involve the remodeling of Larkfield Manor catering hall.
Police initially said the road closure was in East Northport but later said it was actually on the Commack/Elwood border.