Hurricane Dean strengthened into a Category 5 storm capable of catastrophic damage Monday night as its first rain and winds began hitting the coasts of Mexico and Belize. Thousands of tourists fled the beaches of the Mayan Riviera as the fast-moving storm roared toward the ancient ruins and modern oil installations of the Yucatan Peninsula. Mexico's state oil company, Petroleos de Mexico, said it was evacuating all of its more than 14,000 offshore workers in the southern Gulf of Mexico, which includes the giant Cantarell oil field. Dozens of historically significant Mayan sites also were emptied, and any metal signs or objects that could go airborne in hurricane-force winds were removed. Dean - which has killed at least 12 people across the Caribbean - quickly picked up strength after brushing Jamaica and the Cayman Islands. By 0035 GMT (8:35 p.m. EDT), it had sustained winds of 257 kph and was centered about 335 kilometers east of Chetumal, Mexico, the US National Hurricane Center said. The eye was expected to strike near Chetumal early Tuesday morning. Category 5 storms are monstrous, and rare - only three have hit the US since record-keeping began. Cancun's swank hotels, many of them newly hurricane-proofed, seemed likely to be spared a direct hit. Oil rigs are made of steel, designed to withstand damaging winds. And ancient Mayan sites like the stunning seaside temples at Tulum, about 125 kilometers north of Chetumal, were built from solid limestone. Dean appeared to be bearing down on the Yucatan's most vulnerable population - the Mayan people - many of whom have seen little of the riches from oil or tourism, and still live in traditional wooden slat huts in small settlements all over this low-lying area. A large storm surge could push seawater deep inland, and Dean's heavy rains could inundate the swampy region. "Yes, we are afraid," said construction worker Pedro Kanche, a Mayan, as he nailed boards against the windows of a shop in Cancun late Sunday. "The truth is that a lot of people lost jobs" during Hurricane Wilma in 2005, "and tourism still hasn't recovered." Tulum shopkeeper Israel Martinez, speaking as he too nailed up boards across store windows Monday, expressed the kind of cold logic that rules a coast marked by contrasts of poverty and wealth, Indian and outsider. "The less the tourist centers are affected, the faster the recovery will be," said Martinez, 28, a non-Indian who has lived in Tulum for 15 years. "Nobody wishes ill upon their neighbors, but if some of these smaller towns are hit, they can be repaired faster," without affecting the area's lifeblood, tourism. A hurricane warning was in effect from Cancun all the way south through Belize, as well as the Yucatan's western coast. All hospitals were closed in Belize City, the country's biggest, and authorities urged residents to leave, saying Dean is too strong for their shelters. Meteorologists said a storm surge of four to six meters was possible at the storm's center. The storm was expected to slash across the Yucatan and emerge in the Gulf of Campeche, where Petroleos de Mexico decided Monday to shut down production on the offshore rigs that extract most of the nation's oil. Shutting the area's 407 oil wells will result in a production loss of 2.7 million barrels of oil and 2.6 billion cubic feet of natural gas a day, Pemex said. Of that, about 1.7 million barrels of oil a day is exported from three Gulf ports, where Pemex was loading the final tankers before shutting them as well. Central Mexico was next on the storm's path, though the outer bands were likely to bring rain, flooding and gusty winds to south Texas, already saturated after an unusually rainy summer. At the southern tip of Texas, sandbags were distributed in the resort town of South Padre Island, and residents were urged to evacuate. "Our mission is very simple. It's to get people out of the kill zone, to get people out of the danger area, which is the coastline of Texas," said Johnny Cavazos, Cameron County's chief emergency director. In Mexico, the Quintana Roo state government said about two-thirds of the 60,000 tourists in the Cancun area had left. Some camped overnight at the city's airport to ensure a flight out. Many others were turned away. Eric Morovich of Orange County, California, waited outside Cancun's airport after trying unsuccessfully to book a ferry, rent a boat and charter an airplane. "I'm just hoping that we get out in time," he said. "We've got two little kids back in the States." Along Cancun's tourist strip, the skyline is still marked with cranes used to repair the damage of Wilma, which caused $3 billion in losses. Dean could be even stronger than Wilma, which stalled over Cancun and pummeled it for a day. The fast-moving Dean was passing farther south, and was likely to deliver a brief but powerful punch to the Maya heartland. That area stretches from the stunning seaside ruins of Tulum south to the growing beach resort at Mahahual, where authorities evacuated hundreds of tourists on Monday. Between the two lies the 1 million-hectare Sian Kaan nature reserve, with a 1,200-year-old network of Mayan canals. Government anthropologists said they were preparing 13 archaeological sites for the storm, pruning trees and removing signs and vegetation that strong winds could turn into damaging projectiles. Cancun still could face destructive force winds, since the storm swirled over 195,000 square kilometers, twice the size of South Korea (about the size of South Dakota). "We're leaving. You don't play around with nature," fisherman Maclovio Manuel Kanul said, pulling equipment from his beachfront fishing shack near Cancun. "We still haven't been able to recover from Wilma, and now this is coming." In Belize, government evacuated thousands of people from the country's main tourist resort, San Pedro on Ambergris Caye, and nearby Caye Caulker, said national emergency coordinator James Jan Mohammed. People were urged to leave low-lying areas. Authorities evacuated Belize City's three hospitals and were moving high-risk patients to the inland capital, Belmopan, founded after 1961's Hurricane Hattie devastated Belize City. Belize City Mayor Zenaida Moya urged people to leave, saying shelters aren't strong enough to withstand a storm of Dean's size. Dean, the first hurricane of the Atlantic season, raked Jamaica and the Cayman Islands on Sunday, but both escaped the full brunt of the storm. In Jamaica, the storm uprooted trees, flooded roads and collapsed some buildings. Downed utility poles left thousands without electricity or telephone service. Police said two men were killed: one when his house collapsed and another struck by flying debris. Haitian officials on Monday reported two more deaths from the storm, raising the storm's death toll in the Caribbean to at least 12. The worst storm to hit Latin America in modern times was 1998's Hurricane Mitch, which killed nearly 11,000 people and left more than 8,000 missing, most in Honduras and Nicaragua.