Cholera has infected at least 1,052 people in Mozambique's cyclone-hit region, the health ministry said Monday in a new report, marking a massive increase from 139 cases reported four days ago.
The mounting cases represent on average more than 200 cases of new infections each day.
Although hundreds have been taken ill with cholera since last week, only one death has been reported so far, tallies compiled by the ministry showed.
A mass vaccination campaign is due to be rolled out on Wednesday as authorities and aid workers are scrambling to avert an epidemic more than two weeks after a devastating cyclone slammed Mozambique.
Some 900,000 doses of oral cholera vaccines have been ordered and were due to arrive in the impoverished country on Monday.
"Vaccination against cholera begins on Wednesday in Beira," a senior Mozambican health official Ussein Isse said.
The central city of Beira is the worst affected, accounting for 959 out of the total 1,052 cases.
The city of more than half-a-million people recorded 247 cases in 24 hours between Sunday and Monday morning.
Cholera is transmitted through contaminated drinking water or food and causes acute diarrhoea.
Cyclone Idai killed more than 700 people across Mozambique, Malawi and Zimbabwe and hundreds of thousands have been left homeless -- many of whom have been forced to use dirty water supplies.
Experts have warned that the destruction of drinking water sources and lack of sanitation in overcrowded shelters in Mozambique create breeding grounds for waterborne diseases such as cholera.
To control the outbreak, vast quantities of drinking water and water purification units have been delivered to affected areas.
A publicity blitz to raise awareness of the cholera situation is also under way.