A Northwest Airlines jet bound for Beijing was diverted to another Chinese city after a security alert. The passengers and crew were questioned by authorities after landing, the U.S. airline said Friday.

China's official Xinhua News Agency said a threatening note was found aboard the flight from Detroit, but the airline's general manager in China wouldn't confirm the note.

The Boeing 747-400, with 132 passengers and 18 crew aboard, landed Thursday in Tianjin, a port city southeast of Beijing, said John Watkins, Northwest's vice president and general manager for China.

Tianjin is about 75 miles from the Chinese capital.

Watkins cited "security concerns" but wouldn't give any details. He said Chinese authorities interviewed all the passengers and crew, searched all the luggage aboard and inspected the aircraft.

"Nothing unusual was found," Watkins said.

The passengers were driven by bus to Beijing, Huang said.