Northeast China's Heilongjiang province reported four locally transmitted confirmed cases of COVID-19 on Saturday, the provincial health commission said on Sunday.

Among them, the three patients reported in Suifenhe - a 33-year-old female resident, a 6-year-old primary school student and a 4-year-old child - are close contacts of the confirmed case reported on Thursday.

The patient reported in Dongning is a 68-year-old female local resident.

The four cases tested positive for coronavirus on Saturday and then were diagnosed as confirmed cases after expert consultation.

Dongning and Suifenhe are important port cities on the China-Russia border in Heilongjiang.

The city of Dongning has adopted strict measures to preventing local residents from leaving the city starting Sunday.

Except for those patients in severe condition or pregnant women, nobody is allowed to leave the city, the city's epidemic prevention and control headquarters announced.

As of Sunday, the province has reported six local confirmed cases and two local asymptomatic cases after two cases - a 40-year-old constructor working at the customs office in Dongning and a 39-year-old stevedore that worked at a warehouse dealing with imports and exports in Suifenhe – were reported on Thursday.

The province also reported an imported confirmed case on Saturday.

The 52-year-old patient arrived in Xi'an, Shaanxi province, from Russia on Nov 25.

He tested negative for the novel coronavirus five consecutive times during his 15-day quarantine period in Xi'an and returned to Tahe county, Heilongjiang on Friday.

He was found to test positive for the virus during the test conducted after his arrival in Tahe.

Then he was diagnosed as an asymptomatic case.

On Saturday, he was diagnosed as a confirmed case.