Water poured through makeshift barriers on Friday into a Mexican city devastated by floods that has forced hundreds of thousands of people from their homes and caught the government off guard.

Sandbags failed to hold back a murky, brown deluge pouring into a main street in Villahermosa, home to some half a million people and capital of the oil-producing state of Tabasco, which is 80 per cent under water.

At least 500,000 people were made homeless and one person was killed in the worst flooding the swampy state has seen in more than 50 years.

The banks of the Grijalva River, which winds through Villahermosa, burst after days of heavy rains.

When will this finish? said resident Maria de la Luz Robles. This is chaotic and depressing.

The army evacuated most of the city center on Thursday night after a levee broke. Interior Minister Francisco Ramirez acknowledged the disaster took the government by surprise.

The event overwhelmed everyone and that's why we all have to work intensely, he said.

Tabasco Gov. Andres Granier said more than 1 million people, about half of the state's population, were affected by the flooding. Scores called local radio programs pleading to be rescued. Many shelters were evacuated after floodwaters overtook them.

Floodwaters half-covered several giant carved stone heads built by the Olmecs, one of the first great civilizations in the Americas, at the state's La Venta archeological site. Some of the heads are more than 9 feet tall.

Officials have said Tabasco has lost all of its banana, corn and chilies crops.

The floods were triggered by storms that have wreaked havoc in the oil industry along Mexico's Gulf coast but the main oil port of Coatzacoalcos opened on Friday after closing earlier in the week due to the bad weather.

(Reporting by Alberto Fajardo and Luis Manuel Lopez)