The death toll from cholera in Haiti has risen to 644, officials have announced.

Aid workers are still fighting to contain the spread of the disease in the capital Port-au-Prince. Local doctors said they were alarmed at the speed at which new cases were emerging, the BBC reports.

The total amount of infected people is more than 11,000. Haiti's health ministry has announced that these are 1000 more cases, compared to data from Wednesday.

A senior health ministry official said that the epidemic was now "a matter of national security," the BBC reported.

Dan Epstein, spokesman of the Pan-American Health Organization (Paho), has announced that the organization expected 270,000 Haitians to be infected by the disease in "between six months and a year."

"It's hard to predict the impact. But it's very likely that cholera is going to be in Haiti for a while," he told the BBC.

The disease broke out in the Artibonite River valley in central Haiti in mid-October and initially seemed to have been contained, but cases have since soared.

Officials are warning that a sizeable outbreak in Port-au-Prince, where 1.3 million earthquake survivors live in tents, is now likely.