Mexican President Felipe Calderon has pledged the full support of his government to help more than a million people hit by floods in Tabasco state.
Mexico's entire air force is being used in the relief efforts
Mr Calderon said on a visit to Tabasco that the entire air force was involved in shifting supplies to the region where more than 800,000 are homeless.
Some 80% of the state is under water in the worst flooding for 50 years.
Heavy rain is forecast for the weekend and there are concerns that disease could spread in the murky waters.
Rescue workers are trying to help thousands of people trapped in their homes by the floodwaters. At least one death has been reported.
Helicopters and boats are being used to move people stranded on rooftops or pockets of high land, and hospital patients are being flown to neighbouring states.
The state governor has urged anyone who owns a boat to help out.
President Calderon has given special powers to soldiers and police on the ground to maintain order and prevent looting.
He called on private airlines to help with the relief efforts as all roads in and out of the state are cut off by the floodwaters.
After flying over the state, Mr Calderon described the flooding as "not just the worst natural catastrophe in the state's history but, I would venture to say, one of the worst in the country's recent history".
Once the critical stage was over, he said, "we are going to reconstruct Tabasco whatever it takes".
Tabasco governor Andres Granier said that 100% of the crops had been lost.
He drew a comparison to the damage caused by Hurricane Katrina on the US Gulf Coast two years ago, saying New Orleans was "small compared to this".
Tabasco's capital, Villahermosa, and many other towns in the state have been turned into brown lakes with only treetops and roofs visible.
Villahermosa government secretary Humberto Mayans said that more than 100,000 people on the streets had turned the city "into a huge open-air shelter".
A spokesman from Tabasco's ministry of health said there was a shortage of clean water and food.
"Our shelters are packed with people, and we are still running rescues in the flooded areas using helicopters and boats," Dr Garcia Rochin told the BBC.
Red Cross official Max Romero said 650 shelters had been set up on high ground in Tabasco and in neighbouring Campeche and Veracruz states.
The floods were triggered by storms that crippled Mexico's oil industry.
Twenty-one people died last week when storms forced an oil platform into another rig in the Gulf of Mexico.
Flooding has also affected the southern state of Chiapas, where several thousand people have been moved to safety.
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.
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