More than 4 million residents in Xi'an, capital of Shaanxi province, underwent nucleic acid testing for COVID-19 on Thursday after a third round of testing began at 8 am.

All communities, villages and workplaces were closed effective Thursday, and residents have been asked not to leave the city unless "extremely necessary", according to a statement released by the city government.

Long-distance passenger transportation services have been suspended. However, freight vehicles transporting epidemic prevention materials and daily necessities are exempt.

The statement was issued after 127 people tested positive in the second round of nucleic acid testing.

According to Lyu Yongpeng, deputy director of the city's health commission, Xi'an reported 91 new locally transmitted COVID-19 cases from Wednesday to 1 pm on Thursday, bringing the city's total number of confirmed cases to 234 in the current outbreak.

The new confirmed cases included three children under age 3, Lyu said at a news conference. "Xi'an added 31 new medium-risk areas the previous day," Lyu said. The city had one high-risk area and 71 medium-risk areas as of 1 pm on Thursday, he added.

The outbreak has seen the spread of the virus to a number of other cities in Shaanxi and beyond the province.

Three new cases have been reported in Xianyang, three in Yan'an, both in Shaanxi, one in Beijing, 24 in Dongguan, Guangdong province, four in Zhoukou, Henan province and one in Yuncheng, Shanxi province.

Gene sequencing of the infected patients indicated that the strain of the virus is similar to the cases in Xi'an.

All domestic flights to and from Xi'an Xianyang International Airport have been canceled to contain the spread of the virus, local authorities said on Thursday. Three international flights were still operating as of 10 am on Thursday. Many airlines and railway departments have asked passengers to accept refunds or reschedule their trips.

The city's education and other departments have been urged to carefully prepare facilities for postgraduate entrance examinations scheduled to start at Chang'an University on Saturday to ensure the health safety of teachers and examinees. A total of 135,000 candidates are due to take the exam in the city.

Li Qungang, a senior official at the city's commerce bureau, said there are adequate food supplies, including meat, vegetables, and daily necessities in the city.

A housewife surnamed Liu said the lockdown has had little impact on people's lives in her community. "Residents voluntarily keep safe distances while waiting in line for nucleic acid testing," she said.