Cholera has killed 900 people in Angola in the past 10 weeks, says aid agency Medecins Sans Frontieres, with 25 dying in a single day this week.
This is Angola's worst outbreak of cholera for several years
Some 20,000 people are infected in several provinces and measures to contain the epidemic are inadequate, MSF says.
Cholera is spread primarily by contact with contaminated water or food.
Many Angolan homes lack running water and sewerage, after millions flocked to towns and cities amid 27 years of war.
A statement from MSF urged the Angolan government and international relief organisations to do more to stem the epidemic.
"Everybody has been slow to respond," said Richard Veerman, MSF's head of mission in Angola.
"Many factors have conspired to make this cholera outbreak one of the worst ever seen in Angola. But with what we know today there can be no excuse for not doing everything humanly possible to prevent the death toll from climbing much higher."
This week, MSF says it saw an average of 30 newly infected people and one death every hour.
Tuesday this week saw the highest daily toll so far, with 929 new cases and 25 deaths recorded by MSF.
MSF is operating six treatment centres in the capital, Luanda, and one each in the cities of Benguela, Malanje, Ndalatando, and Caxito.
Over the past 10 years, Angola has suffered only minor outbreaks of cholera, mostly in the slums of Luanda.
MSF says this has left the population with low resistance to the disease, which has now spread to other provinces as the peace which has prevailed for the past four years has allowed people to travel outside of the capital.