“Zimbabwe is also procuring more vaccines from China at a preferential price. Zimbabwe is set to purchase another 1.2 million doses from China,” Charamba wrote on Twitter.
That would bring to 1.8 million the number of doses being bought from China.
Charamba was not reachable on his mobile phone for further comment.
Mnangagwa's government has not yet disclosed how much it is paying for the vaccines from China. Authorities in Harare have also said Russia and India have donated 87,000 doses in total.
More than two thirds of Zimbabwe's 35,910 coronavirus infections and 1,448 deaths have been recorded this year, according to a Reuters tally.
Separately, neighbouring Mozambique on Wednesday received 200,000 doses of Sinopharm vaccine donated by China.
India has also pledged to donate 100,000 shots to Mozambique, the government said.
Namibian officials said Beijing would donate 100,000 doses of vaccines and that India would donate 30,000 shots.