The Haitian government has told residents to evacuate quake zones ahead of tropical storm Tomas.

The storm is located about 300 miles southwest of the capital city of Port-au-Prince and is expected to attain hurricane strength.

"If Tomas strikes Haiti as a major hurricane, this has the potential to be one of the biggest disasters in recent memory," said Bill Horan, president of Operation Blessing International. "There are over 1 million vulnerable people living in tents, and there's also an outbreak of cholera-which would only escalate as torrential rains cause flooding, spread disease and contaminate drinking water. It's unfathomable to think what might happen."

Operation Blessing has already mobilized its disaster relief team in case they are needed. A water purification plant on a truck is standing by, ready to deliver fresh water to the island nation's hardest hit areas.

Horan said sanitary conditions in the camps are "marginal," and the recent cholera outbreak "could spread like gasoline thrown into a campfire" if precautions aren't taken.

Operation Blessing is the only humanitarian agency in Haiti with the capability to manufacture chlorine-disinfectant to purify water.

Volunteers have also assembled shelter kits for about 200 families, if needed after the storm.

Find out how you can help Operation Blessing International help the people of Haiti.