A massive rescue operation is under way in the southern Mexican state of Tabasco after rains caused the worst flooding there in more than 50 years.
More than one million people are believed to be affected, with 300,000 thought to be trapped in their homes and more rain forecast in coming days.
Most of the state is under water and its governor has urged anyone who owns a boat to help the rescue operation.
President Felipe Calderon said the situation was "extraordinarily grave".
"It's one of the worst natural disasters in the history of the country," he said in a televised address on Thursday night.
'Just like New Orleans'
Rescuers are using helicopters to try to pluck people from rooftops. Thousands of people are huddled inside their homes or emergency shelters.
The floods were triggered by storms that crippled Mexico's oil industry.
Tabasco Governor Andres Granier said more than half of the state's 2.1 million residents had been affected.
"We have lost 100% of our crops and 70% of the state is under water," he told reporters.
"We are just like New Orleans. All the water that comes in has to be pumped out."
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.
President Calderon has flown to the area and is promising more soldiers and aid.
The state has been placed on high alert.
Oil industry woes
A Red Cross worker in Tabasco state said 70% of Villahermosa was affected and there was an urgent need for basic materials to help the rescue effort.
Those trying to help flood victims needed water supplies, food and mattresses, he told the BBC.
An appeal was being made for boats and ropes, to help navigate the flooded streets and reach stranded victims.
The main priority for rescuers was to try and get all the affected people out, with concerns high because of forecasts suggesting more rain was due, he added.
Twenty-one people died last week when storms forced an oil platform into another rig in the Gulf of Mexico.
Dozens of workers had to leap into the water.
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 reports.
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