Mozambican authorities say the number of cholera cases among cyclone survivors has risen to 271.
The Portuguese news agency Lusa cites national health director Ussein Isse, who initially declared the outbreak of the acute diarrheal disease on Wednesday with just five cases.
The report says so far no cholera deaths have been confirmed.
The cases have been discovered in the port city of Beira, whose half-million residents and especially those in crowded poor neighborhoods are at particular risk.
Doctors Without Borders has said it is already seeing some 200 likely cholera cases per day in the city, where relief workers are hurrying to restore the damaged water system and bring in additional medical assistance.
The World Health Organization has said some 900,000 cholera vaccine doses are expected to arrive on Monday.