Hurricane Ike barreled toward Cuba as an extremely dangerous Category 4 storm on Sunday and was forecast to sweep into the central Gulf of Mexico as a large and powerful storm echoing Hurricane Gustav, reported reuters. Ike's top sustained winds reached 135 miles per hour (215 kph), making it a savage Category 4 on the five-step Saffir Simpson scale of hurricane intensity, the U.S. National Hurricane Center said. Forecasters said Ike could strengthen further before sweeping into Cuba late on Sunday, severely threatening sugar cane fields, the tourist hotels of Varadero and the crumbling colonial buildings of Havana. The densely populated Miami-Fort Lauderdale area in south Florida seemed an increasingly less likely target, but visitors were ordered to flee the vulnerable Florida Keys island chain on Saturday. Ike was forecast to curve into the Gulf of Mexico in the wake of this week's Hurricane Gustav, plowing toward an area that produces a quarter of domestic U.S. oil. Gustav slammed ashore near New Orleans, which was swamped and traumatized by Hurricane Katrina three years ago but largely spared by Gustav. Oil companies had begun returning workers to the offshore platforms that were evacuated before Gustav hit Louisiana on Monday west of New Orleans. But one company, Shell Oil Co. , said on Saturday it had stopped returning workers in case new evacuations were needed. The deeper Ike goes into Cuba, the weaker it will be once it re-emerges over the Gulf of Mexico. But over water it was expected to rapidly regain its former intensity. "In five days there will be a large hurricane in the central Gulf of Mexico," the hurricane center said. Alerts went up across eastern Cuba as residents shivered at the prospect of another major storm a week after Hurricane Gustav devastated parts of western Cuba. Tourists were evacuated from the Guardalavaca resort on Holguin province's northern coast, as were thousands of students picking coffee in the mountains.