BEIJING - China reported on Thursday a decline in locally transmitted COVID-19 cases for the first time this week, and a health official said he expected China's latest outbreak, caused mainly by the Delta variant, to be largely under control within weeks.

A total of 85 new confirmed COVID-19 cases were detected for Aug. 4, down from 96 a day earlier, data from the National Health Commission (NHC) showed on Thursday. Of the new cases, 62 were locally transmitted, versus 71 a day earlier.

China's vice premier Sun Chunlan said on Wednesday the development of the various clusters remained uncertain, and authorities' bid to curb the spread of the virus should overcome "a laxity of mind", the official Xinhua news agency reported.

Some local governments have been called out by Beijing for lowering their guard, leading to the spread of the Delta variant from multiple sources.

Still, NHC official He Qinghua said the virus situation was largely controllable.

"As long as local authorities strictly implement various (virus control) measures, the outbreak can be largely controlled within two to three incubation periods," He told a news conference on Thursday.

The latest NHC guidelines published in April stated that an incubation period for COVID-19 can be as long as 14 days, but is usually three to seven days.

"Nationwide, it is possible that new outbreaks will occur in other areas, and various local authorities should strengthen their monitoring," He cautioned.

Dozens of Chinese cities, including Wuhan, Beijing and Shanghai, have reported new cases since late July, including those with symptoms and those without, in what officials say was the most serious outbreak since the peak of China's epidemic in spring last year.

To deal with the infections, some cities have initiated multiple rounds of mass testing to identify carriers. Inter-city travel restrictions have been imposed, and public places of gathering including entertainment venues have been either shut or restricted.

The National Immigration Administration has stopped approving non-essential and non-urgent trips outside of China by ordinary Chinese nationals, an official said on Wednesday.

Capital Beijing, one of more than a dozen cities reporting the Delta variant in locally transmitted cases, has cut passenger volume at multiple subway stations during the morning rush hour to prevent the virus's spread.

It has also said large exhibitions and events during August will be cancelled, unless they are necessary.

China reported on Thursday 54 new asymptomatic coronavirus infections for Aug. 4, which it does not classify as confirmed cases, compared with 27 a day earlier.

No new deaths were reported.

As of Aug. 4, mainland China had recorded 93,374 confirmed cases, with the cumulative death toll unchanged at 4,636.

(Reporting by Ryan Woo, Liangping Gao and Roxanne Liu; Editing by Muralikumar Anantharaman and Bernadette Baum) ((Ryan.Woo@thomsonreuters.com;))