The death toll from this cholera outbreak rose to 20 on Tuesday, from just five reported late last week.
State media says two of those who died were children at a primary school in Harare's western Glen View suburb -- the epicentre of this outbreak.
Twenty other children at the school have been taken ill.
So far more than 2,300 people have been infected with the disease.
It’s believed the outbreak came after borehole water relied on by some residents in Glen View and the neighbouring Budiriro suburb was contaminated by sewage.
Most residents of the capital depend on wells or boreholes as many suburbs haven’t received treated municipal water for years.
Zimbabwe’s new health minister, Obadiah Moyo, who only took his oath of office this week, said the declaration of an emergency would help officials quickly contain the outbreak.
The authorities say isolated cases of cholera have now shown up in another four of the country's 10 provinces.
Memories are still fresh of a cholera epidemic that swept through the country 10 years ago, killing 4,000 people and sickening tens of thousands of others.