BEIJING — A Chinese-born professor at an Australian university who has often criticized Beijing’s crackdown on political dissent has been barred from leaving China and is being questioned by state security officers as a suspected threat to national security, his lawyer said on Sunday.

The confinement of Feng Chongyi, an associate professor at the University of Technology Sydney, or U.T.S., unfolded over the weekend while China’s premier, Li Keqiang, visited Australia to promote deeper trade and diplomatic ties. Professor Feng’s case could cloud those ties.

The lawyer, Chen Jinxue, said Professor Feng had not been arrested or formally charged.

The professor has been staying in a hotel in Guangzhou, a city in southern China, and has been repeatedly questioned by national security officers after being stopped by entry-exit checkpoint officials on Friday and Saturday from taking flights back to Australia, Mr. Chen said from Guangzhou, where he was accompanying Professor Feng.

“He’s been told he’s suspected of involvement in a threat to national security,” Mr. Chen said by telephone, adding that Professor Feng declined to comment.