All cross-border truck drivers entering and leaving the Zhuhai Special Economic Zone in Guangdong province are now required to show negative results of a coronavirus nucleic acid test taken within 12 hours.

The new measure was introduced on Wednesday after four Macao residents' test results came back positive on Tuesday. It aims to prevent and control the spread of coronavirus in the southern metropolis, which borders Macao, according to a statement by the city's anti-virus headquarters on Wednesday.

Meanwhile, Zhuhai has launched a citywide testing campaign and has ordered all the movie theaters and similar entertainment venues to suspend business temporarily, the statement said.

On Tuesday, departments in Zhuhai started tracing the activities of three Macao residents in the wake of positive nucleic acid test results. Various departments also expanded screening of people at the city's airport, exit and entrance ports and other key venues.

A couple from Macao were found positive after routine tests when they arrived in the city on Tuesday. Their daughter also passed through the Zhuhai airport from Macao and took a flight to Xi'an, Shaanxi province, on July 19. She returned to Zhuhai on July 24 and then took a bus back to Macao.

The daughter and a son now living in Macao were tested and found positive for the coronavirus.

The statement urged anyone who had contact with the parents and daughter to report to relevant departments and be tested to prevent the coronavirus from spreading in Zhuhai. Mass testing has also been undertaken in areas of Zhongshan bordering Zhuhai in the western part of the Pearl River Delta.

In Guangzhou, Guangdong, all bus passengers are now required to have their body temperature measured and show a green health code.