Rwanda has re-introduced tough lockdown measures in its capital Kigali after a surge in coronavirus cases.

The government has also banned movement into and out of the city, except for essential services and for tourists, it said, citing a jump in the number of cases found in a given sample of tests, known as the positivity rate.

"All employees, public and private, shall work from home, except for those providing essential services," the government said in a statement.

Rwanda, which has 11,259 cases of the disease caused by the coronavirus and 146 deaths, said the number of tests returning positive results for Covid-19 has tripled to 7.7% from 2.6% at the start of this month.

African nations are grappling with a second wave of the novel coronavirus, infections rising to at least 3.3 million and 79,500 deaths so far, a Reuters tally showed.

Of every 100 infections reported around the world, about 5 are from African nations, up from 3.4 in October, the data showed.

Businesses in Kigali will shut down, the government said, except for those dealing with essential services like food, medicine and fuel.

"Citizens are urged to significantly reduce social interactions and limit movements," it said.