BEIJING: A Chinese city near the border with Myanmar has imposed a lockdown after six coronavirus cases were reported Wednesday -- the first significant cluster of Covid-19 disclosed in almost two months.

Three asymptomatic cases in Ruili, a city of over 210,000 people, were also recorded as Myanmar nationals, aged between 24 and 28, according to health authorities in Yunnan province.

Ruili is a major crossing point from Muse in neighbouring Myanmar, which has seen escalating unrest since a February 1 military coup, raising fears that people may flood across the border if the violence intensifies.

On Wednesday, Yunnan health authorities in China warned they would "severely crack down on illegal border crossings and organisers or harbourers", although they did not directly link the outbreak to irregular movement from Myanmar.

Ruili will also test all its residents for the virus, and everyone will go under "home quarantine" for a week, said an official notice.

This means that residents are not to leave their homes without "special reasons", and only one member of each household can leave to buy daily necessities with permission.

Myanmar's security forces have killed hundreds as they contend with massive pro-democracy rallies across the country, demanding the restoration of the elected government.

The country's borders remain closed to most foreigners, and infections in recent months have been from returning overseas nationals.