Fire swept a downtown Sacramento office building, forcing closure of the city's light-rail line for several hours and causing delays for thousands of morning commuters. More than 50 firefighters were summoned to the blaze in a two-story building near 12th and P streets. No injuries were reported in the fire, which caused extensive damage. Cause of the fire was not immediately known. Streets nearby, including heavily traveled 12th Street, were blocked off, delaying thousands of commuters. Part of the city's light-rail trolley system was shut down for two hours, Regional Transit spokesman Mike Wiley said. About 3,000 train commuters from Sacramento suburbs were dropped off on the outskirts of town and walked or were bused to their offices, Wiley said. "All of the passengers . . . seemed to be taking it in stride," he said.