China's northeastern border with Russia has become a front line in the country's fight against a resurgence of the coronavirus, as new daily cases, while remaining relatively low compared with other global hot spots, rose to the highest in nearly six weeks.

After reporting to have largely stamped out the domestic transmission of the disease, China has been slowly easing curbs on movement as it tries to get its economy back on track, but there are fears that a rise in imported cases could lead to a second wave of the coronavirus, which causes COVID-19.

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A total of 108 new cases were reported in mainland China on Sunday, up from 99 a day earlier, marking the highest daily tally since March 5.

Imported cases accounted for a record 98 of those infections and half of those imported infections involved Chinese nationals returning from Russia's Far Eastern Federal District, home to the city of Vladivostok, who had re-entered China through border crossings in Heilongjiang province, according to authorities.

Meanwhile, the Chinese cities along the Russian frontier have been tightening border controls and imposing stricter quarantines in response to the threat.

The city of Suifenhe and the provincial capital of Heilongjiang, Harbin, are now mandating 28 days of quarantine as well as nucleic acid and antibody tests for all arrivals from abroad.

"Our little town here, we thought it was the safest place," a resident of the border city of Suifenhe, who only gave his surname as Zhu, told the Reuters news agency.

"Some Chinese citizens - they want to come back, but it's not very sensible, what are you doing coming here for?" he said.

Similar restrictions to Wuhan

China's border with Russia remains closed, except to Chinese nationals, and the land route through Suifenhe has become one of the few options available for people trying to return home after Russia stopped flights, except for evacuation, to China.

The streets of the city were virtually empty on Sunday evening due to restrictions of movement and gatherings announced last week, when authorities took preventive measures similar to those imposed in Wuhan, the central Chinese city where the first infections from the new coronavirus appeared in December.

The total number of confirmed cases in mainland China now stands at 82,160. Though the number of daily infections across China has dropped sharply from the February 12 peak, when more than 15,000 cases were reported in a day, China has in recent weeks seen the daily toll creep higher after hitting a low trough March 12.

In Shanghai, authorities found that 60 people who arrived on Aeroflot flight SU208 from Moscow on April 10 have the coronavirus, Zheng Jin, a spokeswoman for the Shanghai Municipal Health Commission, told a news conference on Monday.

Residents in Suifenhe said a lot of people had left the city fearing contagion, but others put their trust in authorities' containment measures.

"I don't need to worry," Zhao Wei, another Suifenhe resident, told Reuters. "If there's a local transmission, I would, but there's not a single one. They're all from the border, but they've all been sent to quarantine."