Safety checks have cleared both of the two Air China flights that were subject to threatening telephone calls before takeoff on Tuesday, the country's flagship carrier told Xinhua.

No dangerous items were found on either flights -- CA4111, from Lhasa to Beijing via Chengdu, and flight CA1578, from Nanchang to Beijing, Air China said.

Both flights were due for takeoff on Tuesday evening, the carrier said in two separate posts on its official account on Weibo.com, China's Twitter-like microblog.

They were subject to the threatening calls from unidentified sources, said Ding Yue, Air China spokesman.

Flight CA4111 was scheduled for takeoff from Lhasa at 4 pm while CA1578 was due to leave Nanchang at 6:05 pm.