Hundreds of thousands of Mexicans fled devastating floods along the swampy Gulf coast, with many leaving for other parts of the country amid reports of looting and warnings of a possible health crisis.

President Felipe Calderon, who surveyed the disaster zone from the air on Friday, called the flooding one of Mexico's worst recent natural disasters.

A week of heavy rains caused rivers to overflow, submerging at least 80 percent of the oil-rich state of Tabasco. Much of the state capital, Villahermosa, looked like New Orleans after Hurricane Katrina, with murky water reaching to second-story rooftops and desperate people waiting to be rescued.

At least one death was reported and nearly all services, including drinking water and public transportation, were shut down as more than 900,000 people in the state of 2 million had their homes flooded, damaged or cut off.

Food was extremely scarce, and federal Deputy Health Secretary Mauricio Hernandez warned of possible outbreaks of cholera and other waterborne diseases.

"With so many people packed together there is a chance that infectious diseases could spread," Hernandez said.

About 150 of the state's hospitals and clinics were out of commission due to the flooding.

Calderon ordered the armed forces and federal police to maintain order and prevent looting, but local radio reported that desperate residents had begun sacking markets for supplies.

Roads not covered by water were clogged with long lines of cars as residents tried to leave Villahermosa for less affected areas. Half of the city's gas stations were out of service, but the exodus appeared to be orderly with no reports of violence.

Villahermosa resident Mauricio Hernandez, 27, who is not related to the federal official, paid a taxi to bring him to Cardenas, a city 50 kilometers (30 miles) east of Villahermosa. From there he said he planned to hop a bus to the port city of Coatzacoalcos.

"We are leaving because we cannot live like this," Hernandez said. "We don't have any water, and the shelters are full. Where are we going to go?"

At least 6,000 people fled to shelters in Coatzacoalcos and nearby Minatitlan, both in neighboring Veracruz state. Thousands more holed up in private homes and hotels.

Alfonso Morales, mayor of Coatzacoalcos, told The Associated Press that Veracruz Gov. Fidel Herrera had sent state buses to Villahermosa to collect flood victims.

Rain gave way to sunshine Friday but forecasters predicted more precipitation in the coming days. While many rivers in the Tabasco mountains had stabilized Friday night, the Grijalva river in the state capital was still rising and was 69 centimeters (27 inches) above its highest recorded level, the National Water Commission said in a statement.

The flooding was not related to Tropical Storm Noel, which pounded the Caribbean.

In Villahermosa, tens of thousands of people were still stranded Friday on rooftops or inside the upper floors of their homes. Rescue workers used tractors, helicopters, jet skis and boats to ferry people to safety, while others swam through poisonous-snake-infested waters to reach higher ground.

Cell phone service in the area was cut off Friday night and ATM machines were under water in the city center, where computers from flooded office buildings floated through the streets, Mexican television network Televisa reported.

Mexico rallied around the disaster, with people across the country contributing money and supplies. Television stations dedicated entire newscasts to the flooding.

Even though Friday was the national Day of the Dead holiday, banks remained open to accept donations for flood victims.