A Chinese city near the border with Myanmar has imposed a lockdown and started mass testing after three coronavirus cases were reported, with officials rushing to curb another outbreak.

It is the second time in four months that Ruili, home to more than 210,000 people, has been locked down after the discovery of cases imported from Myanmar.

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 will try to flood across the border into China to escape the violence.

One of the three infected patients was a Myanmar national, according to health authorities in Yunnan province.