Firefighters, their equipment reaching up only a dozen or so floors, could do little to contain the blaze, a spectacular wall of flames reflected in the glass skin of the adjacent CCTV tower.

The CCTV complex was an expensive trophy of the pre-Olympics building boom, the result of many billions of dollars that the Communist Party had devoted to making Beijing a city of the future. The main CCTV tower appeared untouched by the fire.

The 241-room hotel, which had been due to open this summer, was unoccupied at the time, hotel executives said.

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According to Chinese television, the fire began at 8:27 p.m. Monday, although witnesses said they spotted flames as early as 7:45 p.m. Within 20 minutes, they said, the fire had spread from the lower floors to the building’s crown. Smoke drifted across the night sky, obliterating a full moon.

The authorities blocked off a thoroughfare known as the Third Ring Road, which runs adjacent to the complex. Subway cars running underneath the site were briefly halted, stranding thousands of passengers. Frantic police officers tried to shoo away huge crowds as sirens wailed and fireworks lighted up the skyline . People watching noted that the timing of the fire, at the end of the spring festival, was inauspicious.

The city had been crackling with fireworks for the annual Lantern Festival, the final day of the two-week Chinese New Year holiday.

A spokesman for Mr. Koolhaas’s firm in Rotterdam, the Office for Metropolitan Architecture, called the fire “a great tragedy.” The spokesman, Stefan Petermann, said the firm had won the competition for the building in 2002; groundbreaking took place in 2004, and the building was due to be completed this May.

As they stood gaping at the blaze, many people said the fire would be widely interpreted as a poor omen for the coming year.

Fan Wenxin, 20, a waiter who works a few blocks from the complex, rattled off a litany of disasters that have shaken China in recent months, among them the Sichuan earthquake, the riots in Tibet and a drought that has left Beijing and much of northern China without precipitation for more than three months. “This does not bode well for the new year,” he said.