LONDON, May 11 (AlertNet) - Some 12,000 people in central Uruguay have been driven from their homes by the worst flooding to hit the country in half a century, according to the United Nations, and forecasters say the rain is likely to persist.

Most schools in the area are closed, electricity and phone lines are down, farm land is submerged, water supplies are contaminated and sewage systems flooded, the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) said in a statement.

Thirty thousand people have been left without access to clean drinking water, and OCHA said there was a risk from water-borne diseases in this small South American nation, sandwiched between Argentina and the southernmost tip of Brazil.

Water is being trucked to the provincial capital of Durazno, where the Yi river overflowed, flooding the town's water supply.

Thousands of families have been evacuated to sports halls and municipal buildings and more than 110,000 people have been affected overall by flooding in seven of the country's 19 departments.

"The number of people affected by this flooding is expected to rise further, especially as flood waters reach lower-lying areas", OCHA said.

The Uruguayan parliament declared a state of emergency on Wednesday, and the United Nations said the government had requested its assistance to cope with the disaster centred on the departments of Durazno, Soriano and Treinta y Tres.

Thousands of houses - as well as local government buildings - have been damaged in the floods. OCHA said the majority of people suffering from the disaster were poor or from groups that are especially vulnerable in emergencies, such as women, children and the elderly.

Uruguay's President Tabaré Vázquez visited the worst-affected department, Durazno, where 6,000 people have been evacuated. The departments of Tacuarembo, Florida, Cerro Largo y Rocha have also been hit.