PORT-AU-PRINCE – With the United Nations and aid agencies still scrambling to provide adequate shelter for those displaced by the earthquake, the potential for a second major crisis looms with the imminent arrival of torrential rains.

A woman stands next to makeshift tents at a camp set up for earthquake survivors left homeless in Port-au-Prince, Tuesday Feb. 16, 2010, one month after a magnitude 7 earthquake struck Haiti. (AP Photo/Ramon Espinosa) More than 200,000 people in Port-au-Prince are living in makeshift camps that sit on flood plains, ahead of a rainy season that typically begins in earnest in April.

But work only started Monday preparing the first of five new sites outside the city where those most at risk could be relocated.

And the Haitian government is still in negotiations to purchase or lease three of those sites from their private landowners, UN officials say.

It generally takes 4 to 6 weeks to prepare a new site, which includes setting up drainage and sanitation facilities.

"It's a huge challenge," says UN spokesperson Kristen Knutsen. "It's going to be a massive campaign."

The UN hopes to have the first new site ready by April 15.

In an average year, this part of Haiti gets close to 400 mm of rain during April and May.

The UN has identified 21 existing camps in the city that are at varying degrees of risk. No estimates were as yet available on how many people could be similarly vulnerable elsewhere in Haiti.

Some at-risk sites could be stabilized with berms and other ways of diverting floodwaters, allowing some or all of the inhabitants to stay if they wish, depending on the site.

Others have been deemed completely unsafe, but UN officials refuse to identify those sites – or the number of people affected – for fear of creating panic.

In total, the new camps outside the city will only have the capacity to take in about 100,000 people.

So the UN is also encouraging those in flood-threatened camps to consider other options. These include moving in with friends or relatives, or going back to the original site of their ruined homes and erecting new shelters there.

Yet there could be other complications.

Many of the concrete floodways that do exist within the city, ones aimed at carrying heavy rainwater safely away, are now filled with all manner of refuse as impromptu dumpsites.

The magnitude-7 quake hit Haiti Jan. 12.