The flight left Changsha, capital of the central province of Hunan, at 8:40am en route to Beijing. It landed in Zhengzhou, the capital of neighbouring Henan province, just over an hour later after the man threatened the crew member.
"The incident was successfully dealt with by 1:17pm, and passengers and crew members are safe," according to a statement from the Civil Aviation Administration of China, which said a man used a pen as a threatening device.
A photo posted by China News Service showed a handful of firefighters standing in front of a row of fire trucks outside Zhengzhou airport.
"I think someone uttered a cry, which woke us. Everyone was sleeping... it was a woman's cry. Nobody knew what was going on," one passenger recounted, according to a video produced by Tencent News and Beijing News.
The crew kept passengers calm and in their seats, he said.
Another passenger said flight attendants told passengers they had to land at a different airport but she had not heard of anything amiss.
"We exited from the back so we didn't see whatever happened in the front, and didn't hear anything either," she said.
Authorities have not yet released further information about the man's motives or what happened to him.