China reported its biggest daily jump in new COVID-19 cases in more than two months, as a city on the border with Myanmar in southwestern Yunnan province accounted for all new local cases.

Ruili’s local government put residents in its urban area under home quarantine, launched a massive testing drive and began restricting people from leaving and entering the city from last week after reporting COVID-19 patients.

The city accounted for all of the 15 new local cases reported on April 4. The total number of new COVID-19 infections, including imported infections originating from overseas, stood at 32, marking the highest total since Jan. 31.

Genetic analysis of the cases discovered in Ruili suggest the new local infections stem from viruses imported from Myanmar, state media reported. Of the new patients reported in the city, 11 of them were identified as Myanmar citizens.

Ruili is a key transit point for Yunnan province, which has struggled to monitor its rugged 4,000 km (2,500-mile) border with Laos, Myanmar and Vietnam for illegal immigration amid a wave of unauthorized crossings last year by people seeking a haven from the pandemic.

On Monday evening, city authorities announced three high risk and six medium risk areas in Ruili as of 7pm local time (1100 GMT), reported state broadcaster CCTV.

CCTV also reported that Ruili would conduct a second testing drive round from April 6 onwards, and that residents who had visited Jiegaoyu City, a jade market in one of the high risk areas, between March 15 and 29 would need to be quarantined at home.

Local authorities have also began a vaccination drive in Ruili in a bid to contain COVID-19 and build up herd immunity in the city.

The number of new asymptomatic cases, which China does not classify as confirmed cases, stood at 18, matching the total from a day earlier.

The total number of confirmed COVID-19 cases in mainland China now stands at 90,305, while the death toll remains unchanged at 4,636.