A week of heavy rains unleashed massive flooding Wednesday in southeastern Mexico, where tens of thousands fled the rising waters for shelters in Tabasco and Chiapas states. At least 20,000 people had sought shelter in Tabasco's oil-rich capital of Villahermosa, where floodwaters reached the rooftoops of homes, and Gov. Andres Granier was urging residents to evacuate. "If they do not leave, I'm going to order them out by force," Granier told reporters in an interview broadcast on the Televisa television network. The flooding also apparently caused the soil supporting a 25-centimeter natural gas pipeline to give way and spring a leak, officials from the state-owned company Petroleos Mexicanos, or Pemex, said. Tabasco state officials said the pipeline had exploded, but that there were no deaths or injuries. Water also crept up around the huge stone heads of an Olmec Indian archaeological site in Tabasco.