BEIJING — Hundreds were evacuated today from the massive building that will house broadcasting facilities for the Beijing Olympics, fearing there was a gas leak after people smelled a strong odor. But authorities later said it was a false alarm and the smell probably came from building materials or chemicals.

Authorities told workers it was safe to go back in and there were no reports of injuries.

John Barton, the director of sport for the Asia-Pacific Broadcasting Union, said he was in his office at the International Broadcast Center when people began running down the halls and telling occupants to clear out. He said no alarm sounded.

"The gas was swirling down the corridor and the emergency drill, if there is one, wasn't followed," Barton said.

"Ladies were running up and down the corridors saying 'Get out of the building,"' he added. "I stepped out of my office and I thought it was some kind of joke — no sirens, no speakers, nothing."

Others at the scene also said there was a strong gas smell in the building before it was evacuated. Firefighters went in along with at least one emergency worker dressed head-to-toe in an orange hazardous materials suit.

But Gao Changli, the executive venue manager of the International Broadcast Center, said the odor came from building materials or liquids. He said there was no gas leak.

The 970,000-square-foot building opened a few weeks ago and is a short walk north of the two iconic venues for the Aug. 8-24 Beijing Games: the Bird's Nest National Stadium and the Water Cube swimming venue. It will house thousands of broadcasters when the games start.

The evacuation is sure to cause jitters among Chinese government officials, who have clamped down hard on security around the games and say openly that terrorism poses the largest threat to the games.

Fernando Pardo, head of sports for the European Broadcasting Union, said in a telephone interview from outside the building there was no public announcement about evacuation.

"They didn't tell us anything," said Pardo. "There was some guy shouting in the corridor and obviously we evacuated. It was the smell of gas. There was the smell of gas when I left my office."

Wang Jue, a Beijing Olympic volunteer, said he was eating in the building when he was told to get out. He said he did not smell gas.

"I didn't hear any alarms go off, so no one thought it was a real evacuation," he said. "I thought it was either a joke or a test run."