A smoky fire broke out on the 86th floor of the Empire State Building Friday and shot up an airshaft to the 102nd floor of the 57-year-old landmark, knocking out at least seven radio stations and jamming traffic.

No serious injuries were reported, and some 1,500 tourists were cleared from the building's two observation decks without incident, officials said.At least seven radio stations that transmit from the spire of the art deco skyscraper were briefly knocked off the air.

The two-alarm electrical fire began in a panel at the foot of a utility shaft on the 86th floor about 1 p.m. and spread to the 102nd floor - the top of the building - where the enclosed observation deck is located, said Fire Department spokesman Efrain Parrilla.

The deck was cleared, as was the open deck on the 86th floor, and scores of sweltering tourists milled around in 93-degree heat on the street in front of the building, squeezed between fire engines and police lines.

The blaze created a 20-block traffic jam on Fifth Avenue and turned midtown traffic into a mire of honking taxis, trucks and cars overheating on the blistering streets.

Police closed off 34th Street between Madison Avenue and Broadway and fire vehicles choked the roadway in front of the 57-year-old building.

Four firefighters suffering smoke inhalation were treated at hospitals and released and three were treated at the scene.