Heilongjiang province reported 11 new locally transmitted confirmed cases of COVID-19 on Monday.

All the cases were found in Harbin, provincial Health Commission officials said on Tuesday. Three of those were reported in the city's Songbei district; the other eight were detected in Bayan county, a statement said.

An investigation found that the confirmed cases in the recent outbreak were in an early stage, said Wang Yan, assistant director of the Harbin Center for Disease Control and Prevention, at a news conference.

"However, the source of the infection is still not clear," she said. "The infection was transmitted through different weddings and banquets, indoor games, living together and dinners. There are clear epidemiological associations between the cases. ... The spread of the virus is very fast as it is highly contagious."

She urged local residents not to leave the city, especially over the coming National Day holiday.

"Those who have to leave the city for special reasons should provide negative nucleic acid test results within 48 hours and pay attention to good health practices," she said.

Since the first case in the latest outbreak was reported on Sept 20, Heilongjiang has reported 60 local confirmed cases and five asymptomatic carriers.