A group of Chinese cities have asked their residents to avoid traveling as more case numbers of COVID-19 have been reported across the country.

Fifty-three new locally transmitted confirmed cases and 25 new locally transmitted asymptomatic carriers were reported on the Chinese mainland on July 31, the National Health Commission said on Aug 1.

Of the confirmed cases, 30 were in Jiangsu, 12 in Henan, four in Hunan, three in Yunnan, and one each in Fujian, Shandong, Hubei provinces and the Ningxia Hui autonomous region, the commission said.

Nanjing, capital of East China's Jiangsu province, recorded 14 locally transmitted confirmed cases on July 31. Since July 20, the megacity has reported 204 locally transmitted confirmed cases, including seven patients in serious condition.

"Nanjing has formed a psychological crisis intervention team to help ease residents' anxiety," said Li Jijun, director of the psychology department at the Affiliated Brain Hospital of Nanjing Medical University.

"Anyone experiencing a psychological crisis can contact the hotline center for help," he said.

Also in Jiangsu, Yangzhou reported 12 and Huai'an four locally transmitted confirmed cases on July 31.

Yangzhou has taken strict measures to contain the virus and launched a second round of nucleic acid testing in its downtown areas on Aug 1.

The city has closed all bus, taxi and ride-hailing vehicle services as well as long-haul bus services out of the city since July 31. Passenger flights at Yangzhou-Taizhou International Airport have also been suspended.

Zhengzhou, capital of Henan province, removed directors of the city's health commission and the No 6 People's Hospital from their posts on July 31 for failing to contain the virus. The city, which was recently hit by torrential rains, reported 12 locally transmitted confirmed COVID-19 cases and 20 asymptomatic cases on July 31.

"The virus is highly contagious and has spread quickly in Zhengzhou," said Zhang Ruoshi, deputy director of the Henan Provincial Health Commission.

"Most of the locally transmitted cases in Henan are related to No 6 People's Hospital, which was the city's designated hospital for treating imported COVID-19 patients."

The city of more than 12.6 million is setting up 4,168 sample collection sites to complete citywide nucleic acid testing in three days, starting Aug 1.

"Health experts confirmed that the new cases were mainly caused by the Delta variant," said Zhao Dongyang, deputy director of the Henan Center for Disease Control and Prevention.

In Hunan province, four locally transmitted confirmed cases were reported on July 31－one in Changsha, two in Zhangjiajie and one in the Xiangxi Tujia and Miao autonomous prefecture. Zhangjiajie has barred all residents from leaving their communities in the city.

On Aug 1, Haikou, capital of Hainan province, also reported a locally transmitted confirmed case.

Also on Aug 1, Beijing reported two new locally transmitted confirmed COVID-19 cases and one asymptomatic case, both related to the outbreak in Nanjing.

The three cases were in Fangshan district. The residential community of the confirmed cases and surrounding communities have been closed to the outside, isolating about 9,500 people.

The people infected in Beijing and people from their communities and workplaces should not go outside the capital. Additionally, people from places outside Beijing where infections were found should not go to the capital.

Flights, trains and buses from those places to Beijing have been suspended, the city's top epidemic prevention group made known in a meeting on Aug 1.

Top Chinese epidemiologist Zhong Nanshan said at a summit in Guangzhou, Guangdong province, on July 31 that he was not too worried about Nanjing's recent outbreak, since the city has taken effective measures to contain the virus.

He also suggested that the concept of "close contacts" should be changed in light of the Delta variant.

"We used to consider as contacts the family members, colleagues and people who had a meal or meeting with infected people up to two days before they showed symptoms. But with the emergence of the Delta variant, people who are in the same space, same workplace and same building as infected people four days before they show symptoms should be considered as close contacts," Zhong said.