The fire at the 101-storey Shanghai World Financial Centre was apparently caused by a welding torch which ignited workplace materials, a city government spokeswoman said.
An initial investigation showed that the blaze at the Shanghai World Financial Center in the heart of the city's Pudong financial district was started by welding work, the official Xinhua News Agency said.
Eight fire trucks had been dispatched to douse the fire, which broke out about 4:30 p.m. (0830 GMT) in an elevator shaft on the 40th floor, Xinhua said, citing the Shanghai municipal public security bureau. It was extinguished at 5:45 p.m. (0945 GMT).
No injuries or deaths were reported, the public security bureau said.
The fire was just the latest travail to face the wedge-shaped tower, being built at a cost of US$910 million (EUR 710 million). The concrete, steel, and glass tower is due to be finished in 2008, when its 101 stories will loom 1,614 feet (492 meters) over China's business hub.
For six years after ground was broken at the site in the mid-1990s, the project was little more than a hole in the ground: The Asian financial crisis had virtually obliterated demand for new office space in Shanghai.
After the project was revived in 2003, the builders had to alter a key design feature - a circular cutout near the top - after complaints that it resembled the rising sun on Japan's flag, a symbol reviled by many Chinese because of Japan's brutal occupation of the country in World War II.
And earlier this year, the tower's builder, the Mori Building Co. of Tokyo, were criticized by Shanghai authorities for altering the project's name to "Shanghai Hills" to link it to its other marquee projects, the famed Roppongi Hills and Omotesando Hills complexes.