An Afghan aircraft bound for Urumqi in China's restive Xinjiang region has been turned back, reports from both countries say.
Chinese state news agency Xinhua reported first that the plane had been hijacked, then that it had been the subject of a bomb threat.
An Afghan diplomat said the plane's operators had not been told about a threat, just ordered to turn it back.
Xinhua said the plane later landed in Kandahar, quoting diplomatic sources.
China's state news agency did not give any details of the reported threat to the plane. But it said that armed police and emergency vehicles had rushed to Urumqi airport just in case.
However a press officer for Nato forces in Afghanistan - which control Kandahar airport - told the Associated Press news agency that he had received no report of a plane forced to land.
"That's a significant activity. If something that significant happens we would know about it," Brian Naranjo said.
Reuters news agency quoted an Afghan air traffic official and a police source as saying that there was no threat to the plane - and that it had been denied permission to land over paperwork.
The incident comes a month after about 200 people died in ethnic violence in Xinjiang's regional capital, Urumqi.
Deadly clashes erupted between Han Chinese and the region's Muslim Uighurs, some of whom want greater autonomy from China.
Since then China has maintained a heavy security presence in the region.