New rule was announced on April 20 alongside the gradual lifting of lockdown measures in three main cities.
On Monday, around 500 people in Antananarivo and Fianarantsoa were penalised, police deputy head Christian Rakotobe said.
Antananarivo commissioner Hector Razafindrazaka said 25 people were sentenced on the spot and forced to sweep the capital’s dusty streets.
Images of the embarrassed-looking offenders were widely circulated on social media.
President Andry Rajoelina has made it compulsory to wear face coverings outdoors in the capital Antananarivo, as well as in the cities of Fianarantsoa and Toamasina, to curb the spread of coronavirus.
Authorities warned that citizens leaving the house without face masks would face community service.
“Seventy percent of people on the street respected the rule … because they are scared of having to sweep pavements,” the head of anti-coronavirus operations, Elak Olivier Andriakaja, said on state television.
“Measures were taken before the sanctions fell into place to raise awareness and distribute mouth covers. I think that’s enough and that sanctions must now be applied.”
To date the Indian Ocean island-nation has detected 128 cases of coronavirus. No fatalities have been recorded so far and 75 patients have recovered.