BEIJING (AFP) - A Chinese city near the border with Myanmar has imposed a lockdown after six coronavirus cases were reported on Wednesday (March 31) - the first significant Covid-19 cluster in China disclosed in almost two months.

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

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

On Wednesday, the Yunnan health authorities warned that 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.