HEAVY rain has caused flooding in Haiti, killing at least 13 people as swollen rivers forced people on to roofs and trapped people in cars and homes.

With 1.3 million homeless and many living in makeshift camps with little or no sanitation as a result of January's earthquake, aid agencies have warned of another humanitarian disaster as the rainy season looms.

Several towns and villages in southern Haiti have been flooded since Saturday, a spokesman for the civil emergency unit said. UN troops and Haitian police moved 500 prisoners from a jail in Les Cayes as 1.5 metres of water swamped the coastal city. Witnesses said houses collapsed and people fled for high ground.

“At one point, people had to climb on the roofs of their homes,” Joseph Yves-Marie Aubourg, the government's representative in the region, told Reuters. Five people died when their car was carried away, and others on foot were swept away in the torrent.

Les Cayes largely escaped the Jan 12 quake which devastated Port-au-Prince and killed more than 220,000, according to government figures. Its population was swollen by families fleeing the capital.

The government, the UN, and aid agencies have all raised the alarm about the rainy season, which starts in March or April and continues until autumn.

The scale of Haiti's catastrophe means that even a huge relief effort has not provided adequate shelter to hundreds of thousands of people. There are 415 temporary settlements housing roughly 550,000 quake survivors, according to the Organisation of International Migration. Others are living in rubble or with relatives.

The United Nations aims to provide every family with two plastic tarpaulins by May 1. So far about 40 per cent of the 1.3 million in need have received tents, tarpaulins or shelter toolkits, according to the Red Cross. Even if the UN reaches its target, rains could turn camps into disease-ridden swamps.

Already the stench of human waste is overpowering at settlements like Saint-Louis de Gonzague, which has one portable toilet for 10,000 people.

— The Guardian, London