Medical services would be limited to emergency units at public hospitals, and patients due for treatment at hospitals and clinics, a notice from city authorities said. All entry and exit for elderly homes had also been suspended.
Manzhouli, close to the border with Russia, is China’s largest land port and a major through-point for freight trains, with routes reaching 13 European countries, according to state news agency Xinhua.
This came as China reported five new local infections from the northeastern port city of Dalian and the Dehong Dai and Jingpo autonomous prefecture in southwestern Yunnan province. There were also 35 imported cases, 20 of those symptomatic.
Separately, health authorities in Shanghai said the three cases they identified on Thursday were found to be part of the same Delta variant transmission chain.
The patients were infected after being exposed to an environment contaminated by an imported virus outside the eastern commercial hub, officials said.
The three friends had travelled to the neighbouring city of Suzhou last weekend, where they dined with two others from Hangzhou in Zhejiang province. Those two were classified as close contacts and also tested positive on Thursday evening.
At least three hospitals in Shanghai said they would resume service on Saturday morning. This came after 12 hospitals on Friday shut outpatient and emergency services until further notice to screen “people, places and environment concerned”.
The new cases come after an outbreak of the highly transmissible Delta variant in mid-October infected more than 1,300 people in 21 Chinese provinces, before being contained earlier this month.
The governments of the affected cities had acted swiftly to mass test residents and impose gathering bans.
China has maintained a zero-tolerance policy towards Covid-19, rolling out mass testing, frequent contact tracing, lengthy quarantines and strict border controls.
In late October, China placed three cities under lockdown to stamp out emerging flare-ups. The cities were Heihe on the Russian border; Lanzhou, the capital of Gansu with a population of over 4 million, and Ejin in the Inner Mongolia region.