Mainland China saw its biggest daily increase in COVID-19 cases in more than five months, the country's national health authority said Monday. New infections in Hebei province surrounding Beijing continued to rise, it said.

The government said it was having limited success in curbing an outbreak in Hebei province that surrounds the capital Beijing.

The Hebei outbreak "has not reached a turning point and the risk of further spread remains," according to the official state-owned Xinhua News Agency. Hebei has a population of 75 million,

Hebei vice governor Xu Jianpei reported 40 new locally transmitted cases and six asymptomatic cases in the first 10 hours of Sunday, Xinhua News Agency said.

He said 223 locally transmitted and confirmed cases and 161 locally transmitted asymptomatic cases had been reported since Jan. 2. There were 19 local infections and 40 asymptomatic cases reported between Jan. 2 and Jan. 4, Hebei officials said Jan. 6.

Hebei accounted for 82 of the 85 new China infections reported Jan. 10, the National Health Commission said in a statement Monday.

Hebei went to "wartime mode" Jan. 6 to halt the spread. Officials said most of the new cases were in the capital Shijiazhuang with its 11 million residents.

Local authorities increased mandatory testing. They said they had completed tests on all residents in Shijiazhuang and Xingtai - where the most recent cases were reported. All positive cases have been hospitalized.

Tests were also conducted in Dingzhou and Xinji.

Shijiazhuang locked the city down over the weekend after new cases. Mayor Ma Yujun said it took three days to complete the first round of mass testing in Shijiazhuang. A second round of testing will take place this week.

Travel restrictions have been imposed on the rest of Hebei. Some 5.49 million people have been tested in Hebei since Jan. 6. This includes medical workers and residents of nursing homes, boarding schools, drug rehabilitation centers, prisons and mental health institutions.

On Sunday, there were 87,536 total confirmed cases in China since December, according to data from Worldometer. Deaths were 4,634.