BEIJING — Chinese authorities on May 1 released a report on the clustered COVID-19 cases in Northeast China's Heilongjiang province since April, urging medical institutions nationwide to draw lessons from them.

Clustered cases related to imported cases have occurred in Harbin and Mudanjiang, two cities in the province, since April, said the document made public by the National Health Commission.

The cases involved nosocomial infections in multiple hospitals, featuring a long duration and a large number of confirmed cases, it read, adding that they had a vile social impact and brought new pressure to consolidating the hard-won achievements in the country's epidemic prevention and control efforts.