Tens of thousands of Mexicans were trapped on rooftops and others clung to lightposts today after heavy rains flooded nearly the entire southern state of Tabasco.

At least 500,000 people were made homeless and one person was killed in the worst flooding the swampy state has seen in more than 50 years, officials said.

The floods began last week and now cover 80 per cent of Tabasco, affecting about one million people, officials said.