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.
China's Xinjiang region
A Kam Air plane from Afghanistan, traveling in China's Xinjiang region was not hijacked and did not receive a bomb threat, according to Afghan officials. 

Earlier the Chinese news agency Xinhua reported a plane to be hijacked. Later reports then stated the plane received a bomb threat and was diverted back to Afghanistan, landing in Kandahar. The early reports say the plane was diverted back to Afghanistan after being denied an emergency landing in Ürümqi.

The plane was traveling to China and had been ordered to turn around after the proper paperwork was not in place. Subsequently it was denied a landing in Ürümqi. Upon its return, the plane landed in Kabul after it encountered high winds. It is not known how many people were on board the plane, but no injuries are reported.

A NATO official denied there was an emergency landing  due to a threat and says the Chinese media reports are untrue.

"We are aware of the reports. We have no evidence that this is true. We would know immediately," said the unnamed official.

The Xinjiang region was the scene of a violent uprising by its Uyghur population last month.