Rescuers on Friday battled to reach people perched on rooftops as the worst floods on record in Mexico's southern state of Tabasco left hundreds of thousands of residents trapped.
Television pictures showed people struggling to get to higher ground as rising water levels reached up to their necks.
Others awaited rescue on rooftops, surrounded by floodwater.
Mexican navy crews used small boats to rescue victims of the disastrous floods.
"The event has overwhelmed everybody," Interior Minister Francisco Ramirez Acuna told journalists.
Overnight, military troops evacuated the center of Tabasco's capital Villahermosa after a levy collapsed, and hospital patients in the city of 750,000 were flown to neighboring states as floodwaters continued to rise.
The floods affected more than one million residents, or about half Tabasco's population, and officials said several hundred thousand people were trapped in their homes.
"New Orleans was small compared to this," said state Governor Andres Granier, in reference to the disaster wrought by Hurricane Katrina in 2005, which killed about 1,000 people in the southern US city alone.
Only one fatality was recorded so far in Tabasco, but the floods have caused widespread devastation.
The oil-rich state the size of Belgium is 80 percent underwater, and 850 towns have been flooded, officials said.
And with more rain forecast over the coming days, there is no respite in sight. Stocks of basic supplies are running low amid what officials said was panic buying.
Tabasco "is devastated," Granier said of the 29,000 square kilometer (11,000 square mile) state on the shores of the Gulf of Mexico. "One hundred percent of crops are lost."
About 400 doctors and health workers were deployed across the region to detect any outbreak of infections, according to Tabasco's civil protection agency.
President Felipe Calderon ordered top government officials to travel to Tabasco to coordinate relief and rescue efforts.
He also ordered officials to tighten security measures in Tabasco to prevent looting, and said at a meeting in Villahermosa, he was delegating "maximum authority" to military and police commanders.
He said more than 7,500 security forces were in Tabasco, to participate in rescue operations and to maintain order.
Military troops organized the evacuation of the Villahermosa city center overnight after hundreds of its residents refused to leave their flooded homes amid reports of looting in the city.
"There's no policing," a Villahermosa woman told reporters. "The thieves climb on the roofs and open the doors through there."
The floods began last week when a cold front brought heavy rain that caused the Grijalva, Carrizal and Puxcatan rivers to burst their banks.
Soldiers and state authorities had placed more than 700,000 sand bags along the rivers to prevent flooding, but the water rose above the barriers.
The floods worsened over the past days as authorities drained water from two dams in the neighboring state of Chiapas to prevent them from exceeding their capacity.
About 30 communities in Chiapas were flooded Friday after rivers burst their banks. The floods in Chiapas killed one person and trapped 20,000.