Farm produce markets and buses have become "amplifiers" in the spread of COVID-19 during the latest outbreak in Dalian, Liaoning province, a local disease control expert said.

On Thursday, the city reported three confirmed COVID-19 cases, including one previously reported as an asymptomatic infection, along with 112 asymptomatic carriers, the city's COVID-19 prevention and control headquarters said on Friday.

"It is quite different from previous outbreaks in our city, which reported sporadic cases. The latest one mainly influenced the downtown regions and was amplified through places like farm produce markets," Meng Jun, deputy director of the Dalian center for disease control and prevention, told Dalian Daily on Thursday.

Genetic sequencing found that the cases reported since Aug 26 were highly homologous to those found in Dalian since Aug 20. Preliminary results showed the source was accidental exposure of non-closed-loop management personnel in a centralized isolation hotel for international travelers.

Infected people, reported since Aug 20, had visited the Taoyuan market, a well-known market with fresh vegetables, meat, seafood and groceries.

"Some cases since Aug 26 are owners or customers of the market. Therefore, they belong to the same outbreak, introduced by infected people into the Taoyuan market, which then became an amplifier and spread out," Meng said.

Infections have been rising in Dalian since Sunday.

On Monday, the city's COVID-19 prevention and control headquarters announced restrictive measures including a work-at-home order and calls to avoid unnecessary trips from Tuesday to Saturday to curb the spread of the virus.

Meng said genetic sequencing had identified the virus responsible for the outbreak as a mutation of the Omicron subvariant BA.5.2.1, which is more contagious and harder to discover.

"We see a large proportion of asymptomatic infections and those who do show symptoms have mild ones," she said, adding that the city's epidemic prevention and control measures have achieved initial results.

"The upcoming three to five days is a critical period for us to curb the further expansion of the ongoing COVID-19 outbreak. We need our residents' cooperation to strictly implement all epidemic prevention and control measures, especially staying at home," she said.