HOHHOT, Dec. 1 (Xinhua) -- China's border city of Manzhouli reported four new domestically transmitted COVID-19 cases in the past day, local health authorities said Tuesday.

The new cases were registered from 7 a.m. Monday to 7 a.m. Tuesday in Manzhouli, Inner Mongolia Autonomous Region. Among them, three patients were re-categorized from previously reported asymptomatic carriers, the regional health commission said.

One new asymptomatic case was also reported during the same period in Manzhouli.

As of 7 a.m. Tuesday, Manzhouli has 18 domestically transmitted cases, two asymptomatic cases and two suspected cases. Their 1,045 close contacts have been placed under medical observation.

Epidemiological surveys and source tracing work regarding the cases are underway.

The autonomous region currently has three imported cases.