BEIJING — China on Monday re-imposed anti-coronavirus travel controls on its southern province of Guangdong, announcing anyone leaving the populous region must be tested for the virus following a spike in infections that has alarmed authorities.

Guangdong, which borders Hong Kong, recorded 20 new confirmed cases, all contracted locally, in the 24 hours through midnight Sunday. Guangdong’s numbers are low compared with many places in the world, but the rise has rattled Chinese leaders who thought they had the disease under control.

People leaving Guangdong by plane, train, bus or private car after 10 p.m. on Monday must present results of a nucleic acid test within the past 72 hours, the provincial government announced. It said testing stations for truck drivers would be set up on major roads.

The government of the provincial capital, Guangzhou, a business center of 15 million people, ordered mass testing after locally acquired infections were found beginning May 21. The government said 700,000 people had been tested through last Wednesday.