The US has expelled more than 6,300 undocumented migrants on its Mexico border using emergency powers to curb coronavirus spread, officials say.

The 21 March public health measure lets officials override immigration laws, expediting removal processes.

Critics say the order is being used as an extension of strict immigration policies.

Meanwhile, the number of illegal border crossings has fallen amid travel restrictions across the region.

The emergency public health order issued by the US Centers for Disease Control and Prevention (CDC) bans the entry of foreigners considered to pose a "serious danger" to the spread of communicable disease.

The measure, initially in place for 30 days, was necessary to limit the spread of the disease in crowded places such as border patrol stations or ports of entry, said CDC Director Dr Robert R Redfield. The US has the world's highest number of confirmed infections - more than 460,000 - and nearly 16,500 deaths.