Chinese mainland reported 126 new locally transmitted confirmed cases of COVID-19 on Wednesday, with more than 100 in northeastern areas including Heilongjiang and Jilin provinces, according to the National Health Commission data.

The northernmost province Heilongjiang reported 68 new confirmed cases and 85 asymptomatic carriers on Wednesday, the provincial Health Commission said on Thursday.

Among the cases, 65 confirmed cases and 48 asymptomatic carriers were detected in Suihua city's Wangkui county, where the first asymptomatic carrier associated with the recent outbreak was reported on Jan 10.

One confirmed case was reported in Heilongjiang's capital city Harbin.

The 67-year-old female resident surnamed Tang was a close contact of a confirmed case reported in Daxing district in Beijing, officials said on a news conference on Thursday.

Tang returned to Harbin on Jan 13 by train from Beijing and was diagnosed as confirmed a case on Wednesday.

"We have traced all 70 passengers of Heilongjiang that were in the same coach with Tang," said Liu Yancheng, an official with the provincial health commission. "And information of the other five passengers of other provinces has been sent to related governments." 

He added that work for tracing more than 800 passengers and staff members on the train is underway.

The commission said all the cases were found during medical observation and quarantine as well as the screening of expanded nucleic acid testing.

"After receiving the report that a worker at a food factory in Harbin tested positive for the novel coronavirus on Tuesday, we immediately closed the factory and conducted a comprehensive screening," said Li Jinsong, deputy director of the provincial Administration for Market Regulation. "We also removed all their products in the markets and conducted nucleic acid testing with the cooperation of health commission and center for disease prevention and control." 

"As of Thursday morning, we had collected more than 60,000 samples and received 43,712 results, all showing negative," he added.

Neighboring Jilin province on Wednesday reported 33 confirmed cases and six asymptomatic carriers, according to the provincial Health Commission on Thursday.

The recent cluster infections in Heilongjiang have expanded to more cities and even other provinces.

For example, Shandong province reported one confirmed case and one asymptomatic carrier on Wednesday, according to the provincial Health Commission.

The two patients - a couple living in Pingdu city - left Suihua on Jan 11 and returned to their home in Pingdu on Jan 14 after travelling to Hezhou in Guangxi, the commission said.

They tested negative for the novel coronavirus two consecutive times on Jan 14 and 16, but results of testing on Wednesday came back positive.

After expert consultations, the 38-year-old male case surnamed Zhang was diagnosed as confirmed case and his 40-year-old wife surnamed Wang was diagnosed as asymptomatic carrier.