The authorities in Mexico say as many as 700,000 people have been affected by heavy rains and severe flooding in the south-eastern state of Tabasco.
The state's governor has called on anyone who owns a seafaring vessel to help free the 300,000 people believed to be trapped in their homes.
"We have lost 100% of our crops and 70% of the state is under water," he said.
Rescuers have also been using helicopters to try to reach people stranded on rooftops.
The heavy rains began at the weekend, forcing rivers to burst their banks in the largely low-lying state.
The BBC's Andy Gallacher in Mexico says it is the humanitarian crisis that now concerns the Mexican authorities.
"We are just like New Orleans," Tabasco governor Andres Granier said. "All the water that comes in has to be pumped out."
Mexican President Felipe Calderon, who flew to the area on Wednesday, says the federal government would be sending aid to help the many thousands of people in Tabasco whose homes have been damaged.
The state has been placed on high alert.
So far, one person is known to have died in the floods.
Tabasco's capital, Villahermosa, and many other towns in the state have been turned into brown lakes with only treetops and roofs visible.
Soldiers and rescuers desperately stacked sandbags along Villahermosa's streets.
Sandbags were also placed around several giant heads carved by the Olmecs, an ancient pre-Columbian people, at Tabasco's La Venta archaeological site.
The storms have forced the closure of three of Mexico's main oil ports, preventing almost all exports and halting a fifth of the country's oil production.
Flooding has also affected the southern state of Chiapas, where several thousand people have been moved to safety, Mexico's El Universal newspaper reported.