Beijing (CNN) -- For the second time in as many days, an unspecified threat forced a Chinese airline to divert a flight, raising public concern about aviation safety in one of the world's fastest-growing air travel markets.
A Shenzhen Airlines flight en route to southern boomtown Shenzhen from Xiangyang -- a medium-sized city in central Hubei Province -- was diverted Thursday night to the provincial capital, Wuhan, shortly after takeoff, the airline said.
"At 10:29 p.m. on August 30, 2012, flight ZH 9706 received threatening information after takeoff," the airline said in a short statement posted online. "To ensure safety, this airline diverted the flight immediately and the plane landed safety at Wuhan Tianhe International Airport at 11:22 p.m. Police have been called in to investigate."
Read more: Threats prompt Air China turnaround
The airline did not reveal the nature of the threat or the number of passengers and crew members on board. The aircraft type is listed as an Airbus A320 -- which typically seats 150 passengers in a two-class configuration -- in its timetable.
An anonymous call containing a threatening message prompted the diversion, the Wuhan airport authority disclosed in a statement released online. State media reported that passengers stayed in Wuhan overnight and would travel to their destination on a new flight Friday.
Retweeting the airline statement, many users on Chinese social media sites expressed rising anxiety about flying after two successive incidents and demanded more information from the airlines and authorities.
On Wednesday, an unspecified threat forced New York-bound Air China flight CA 981 to return to Beijing seven hours after takeoff, the Chinese flag carrier said.
Police found nothing suspicious in their investigation of the plane, the airport authority said in statements posted online. State media also quoted police as saying that the initial warning of the threat came from U.S. authorities, who warned China that dangerous goods that may harm the plane and passengers were on board.
The flight took off again at 12:31 a.m. Thursday after a change of crew and arrived in New York at 12:38 a.m. the same day, according to the airline's website.
Beijing-based Air China was also tight-lipped about the nature of the threat and other details. The aircraft involved, a Boeing 747 jumbo jet, seats up to 344 passengers in the carrier's configuration.
Messages and photos posted on Chinese social media sites Wednesday night showed passengers and their luggage being rescreened at the Beijing airport upon landing.
One passenger on CA 981, whose online handle is Kejiwaijiao, said he noticed something was wrong when the flight map on board indicated the plane was headed back to Beijing. When he inquired, he said, flight attendants told him it was a map display error.
"The captain notified us (of the reason) after we safely landed," he wrote on Sina Weibo, China's equivalent of Twitter.
Another passenger, whose Weibo name is Nataliebu, said crew members only told passengers to buckle up and sit tight due to strong air turbulence.
On June 29, passengers and crew members thwarted a hijack attempt on a short-haul flight within the far western Chinese province of Xinjiang. Authorities said six ethnic Uyghur men violently tried to take control of the plane before being subdued. The plane returned to its point of origin safely.
Security is usually tight throughout Beijing Capital International Airport, the world's second-busiest air hub after Hartsfield-Jackson International in Atlanta. More than 78 million passengers passed through the Beijing airport's three terminals last year.