Two planes were grounded at Chinese airports on Tuesday after anonymous threatening phone calls were received, an airline said, a day after a hoax threat forced a plane to make an emergency landing.

Safety checks cleared one of the flights which was originally scheduled to depart Lhasa in the southwestern region of Tibet at 4pm (0800 GMT), state media said. The flight was waiting to take off Tuesday evening.

Another flight due to leave Nanchang in the eastern province of Jiangxi was still undergoing safety checks three hours after its scheduled departure time around 6pm, Air China said.

Both flights were destined for Beijing, the airline added in a statement.

"Before the planes were due to take off, suspicious telephone calls were received on the ground which threatened the flights," it said.

On Monday a China Southern Airlines plane was forced to land at an airport in Lanzhou, capital of the northern province of Gansu, after it received an "anonymous terrorist threat", state media said.

A search of the Boeing 757, which was carrying 186 passengers and 10 crew, turned up no suspicious items and it took off again later in the evening. A man was arrested for allegedly making a hoax threat.