Several flights from Chongqing and Guangzhou were forced to land or delayed on Friday after telephone threats were received, airport authorities said.

Guangzhou Baiyun International Airport was told by police there was a bomb on board a flight that left the city for Shanghai at about 5:30 pm.

The airport authority invoked an emergency plan to force the Spring Airlines flight to land in Fuzhou, Fujian province.

The plane took off again at 7:56 pm from Fuzhou after no bomb was found. The flight was due to land in Shanghai at 9:48 pm.

Flights at Chongqing and Guangzhou airports returned to normal on Friday night, according to China Central Television, which said police in Chongqing and Guangzhou have identified the suspects who made the threatening calls.

Flights leaving from Beijing, Shanghai and Shenzhen were also affected by threatening calls, CCTV reported.

In Chongqing, hoax calls were made concerning a flight to Shanghai on Friday afternoon. It left safely at 8 pm after a delay of more than two hours.

The airport initiated an emergency plan, and conducted security checks again, according to a safety notice it released.

A staff member from China Southern Airlines in Chongqing, who declined to be named, told China Daily that flight CZ8109, due to leave Chongqing for Shanghai at 5:50 pm, had to wait until 8 pm.

"Flights have returned to normal now," she said, adding that three more flights had been affected in Chongqing, including those operated by China Southern Airlines and Spring Airlines.

Chongqing is holding an international trade and investment fair, which has attracted nearly 6,000 companies.

Wang Jing, a passenger traveling from Chongqing to Guiyang on Friday night, was relieved when she heard that all flights had resumed.

"I received a phone call from my family at about 7 pm, saying there was something going on at the airport. I arrived there early, but luckily my flight is about to leave in half an hour — on time," Wang said.

A psychologist attributed the hoax calls to poor education.

"Suspects in such cases usually have lower educational backgrounds. They treat their behavior as a joke," said Li Meijin, a professor in criminal psychology at Chinese People’s Public Security University.

"Some of them are usually psychologically unsophisticated and know little about the consequences of making threats to airlines or airports."

The threats follow the detention of a man accused of making similar threats that led to the grounding of five flights on Wednesday.

The suspect, identified only as Wang, from the Inner Mongolia autonomous region, was taken into custody in a dawn raid on Thursday by police in Shenzhen.

Wang, 26, has confessed to making the threats by phone on Wednesday morning, which led to flight delays and emergency landings, police said.

Zhao Lei and Zheng Xin in Beijing and Ji Jin in Chongqing contributed to this story.