The National Health Commission has sent a team to Shulan, a county-level city in Jilin province that reported multiple domestically transmitted COVID-19 cases over the past few days, said Mi Feng, spokesman for the commission, at a news conference on Tuesday.

From May 7 through Monday, the city reported 15 confirmed cases, all domestically transmitted. The team will assist with treatment and with an epidemiological investigation.

"Domestically transmitted cases and cluster infections are a reminder that there should be no relaxation in the vigilance of anti-epidemic work," Mi said.

According to the local government, the city, which is now under lockdown, has taken measures including limiting traffic and closing amusement parks, libraries and internet cafes.

Vehicles are strictly restricted on roads, with exceptions being made for those transporting daily necessities and farming materials.

Video footage that went viral showed several pesticide sprayers disinfecting empty streets.

Schools that had resumed classes were shut down again, and senior students have returned to their online classes at home.

Residential communities have also imposed stricter rules.

No outsiders are allowed in, and only one person of a household can go out for daily necessities each day.

The gate pass records their name, gender, number of family members, contact information, address and frequency of daily departures and entrances.

Other residents are not allowed out of their community unless they need to see a doctor or handle an emergency.

Zhang Yu, a 24-year-old Shulan resident, told Chutian Metropolis Daily－a newspaper based in Wuhan, Hubei province－that he stored a lot of food at home and hasn't been out for a few days.

"Food supply is sufficient in supermarkets, because no one has ever complained of a shortage," he said.

The local government announced on its WeChat account on Monday that abundant food and materials are offered at normal prices through stable and smooth supply chains.

On Thursday, a confirmed case in Shulan broke the city's streak of no cases reported for 73 consecutive days.

On Saturday and Sunday, 14 new locally transmitted infections elevated the city's risk of epidemic prevention and control from low to high.

Xinhua contributed to this story.