(CNN) -- At least 20 people have died due to torrential downpours in Haiti, authorities said Tuesday, and aid agencies are scrambling to respond to a resurgence of cholera triggered by the heavy rain.
The rainfall has forced residents to evacuate from homes and tent cities, and created a fertile breeding ground for the bacteria that causes cholera.
The Pan American Health Organization warned the situation in Port-au-Prince continues to deteriorate and most cholera treatment centers are working at "full throttle."
The Haitian Ministry of Public Health has reported 321,066 cases since the beginning of the outbreak last October, including 5,337 deaths. The latest numbers available, however, were as of May 29.
Samaritan's Purse, which is one of the many aid agencies that has set up cholera clinics, was receiving more than 300 sickened people a day over the weekend, said Roseann Dennery, the group's communications director.
"We've been hit really hard with rains lately, so we are preparing for more of the same this week," she said.
The areas most impacted by the heavy rainfall include Port-au-Prince and the Nippes region in the south of the country, said Emmanuelle Schneider, spokeswoman for the United Nations Office for the Coordination of Humanitarian Affairs.
At least 20 people in greater Port-au-Prince died in rains that started Monday evening and continued until early Tuesday morning, the country's civil protection department said.
Six people were injured in Monday night's downpour, the department said, and at least 470 families in Port-au-Prince's Cite Soleil slum were affected.
And more rain is on the way.
Additional rain was expected to hit Haiti Tuesday night, Schneider said.
The U.S. Climate Prediction Center has said the 2011 hurricane season is likely to bring a higher than normal number of storms in the Atlantic basin.
Cholera is caused by drinking tainted water and its symptoms can range from mild or even nonexistent to profuse diarrhea and vomiting. It's not difficult to deal with the disease but if left untreated, death from dehydration can come within a matter of hours.
"The situation continues to deteriorate," said Beat Rohr, director of CARE in Haiti. "We never stopped sensitizing the population about the importance of clean water and the need to wash their hands regularly. But it won't be enough."
Journalist Ross Velton contributed to this report.