NEW YORK (AP) _ A smoky fire at NBC's 70-story headquarters early Thursday knocked the local TV affiliate off the air, briefly disrupted the ``Today'' show and caused minor injuries to 13 people.

More than 300 firefighters battled the blaze at the landmark GE Building in Rockefeller Center for more than four hours before bringing it under control.

The fire, which was confined to the fifth through 10th floors, was believed to have started in a 10th-floor electrical closet at the network's local affiliate, WNBC.

Early morning programming for the New York area was knocked out. ``Today,'' which broadcasts from a glass-enclosed studio across the street, began on schedule, but the video signal was interrupted at one point and Katie Couric spent some of the morning co-hosting from the street.

Taping of the Rosie O'Donnell and Maureen O'Boyle talk shows had to be postponed, and the network's evening news show was broadcast from Washington. Conan O'Brien left the studio to tape his late-night talk show outside in front of the skating rink.

Fewer than 100 of NBC's 2,000 employees were in the building when the fire broke out at 4 a.m. All were evacuated.

Thirteen people were treated for smoke inhalation, including at least two firefighters.

The cause of the fire was under investigation. NBC said it may have been started by a generator at a section under construction.

The Art Deco building houses the studios for such programs as ``NBC Nightly News,'' ``Late Night with Conan O'Brien'' and ``Saturday Night Live.'' Tourists know it for the skating rink and the towering Christmas tree outside.