Getting the 1.3 million homeless quake survivors in Haiti under shelter before the onset of the country's wet season in the next couple of months is a top priority, UN and Red Cross officials said Monday.

"We recognize that the rainy season represents a very grave threat to the quake-affected people in the improvised settlements. And the floods in the southwest over the weekend were a reminder of what's to come," Red Cross spokesman Alex Wynter told AFP.

He was referring to inundations that killed at least 13 people and forced the evacuation of 3,000 in and around Haiti's third-biggest city of Les Cayes on Saturday -- a region untouched by January's devastating earthquake.

According to a spokesman for the UN Office for the Coordination of Humanitarian Affairs, Kristen Knutson, 40 percent of those huddled in makeshift camps around the flattened capital Port-au-Prince, or 523,000 people, have received materials to make emergency shelters.

While those efforts were continuing, there were concerns that many of the survivors would be exposed to torrential downpours and flooding when the wet season unleashes its full force come April or May.

"Right now, an estimated 604,000 people are staying in 415 spontaneous settlements of all sizes throughout Port-au-Prince," Knutson said.

"However, many of these spaces were only available because they were public spaces (parks) or flood plains, posing a potential threat to those living there once the rains start."

The UN office was coordinating a voluntary program to have the homeless move back to their neighborhoods, with plans to clear them of debris and install sanitary facilities.

In addition, the Haitian government was identifying locations outside the capital where more durable shelters could be set up, Knuston said -- though that was a medium-term strategy likely to be implemented well after Haiti's heavy rains hit.