A man walks in the rain during the approach of Hurricane Gustav in Batabano, on the southern coast of Cuba, August 30, 2008. [Photo: Reuters]

Related: California Relief Workers Ready to Help against Gustav

Tropical storm Gustav strengthened into a Category 4 hurricane as it churned into western Cuba Saturday and is now on its way to the oil-rich Gulf of Mexico and the U.S. coast.

Gustav, with 240 kmph winds, poured heavy rains, knocked down power lines and uprooted plants as it swept across Cuba's western Pinar del Rio province, the country's main tobacco-growing region.

Authorities have evacuated some 250,000 people in four western provinces. No lives have been lost due to the well-organized evacuation, Cuban officials said.

In the country's Havana province, where the capital is located, the storm emptied streets and severed power lines in many cities. Some 77,000 people have been evacuated across the province.

Forecasters predict the hurricane is likely to strengthen into a ferocious Category 5 as it tears into the Gulf of Mexico.

In anticipation of the deadly hurricane, three-quarters of the offshore oil fields have been shut down in the Gulf, where there are some 4,000 platforms producing a quarter of the United States' crude oil and 15 percent of its natural gas.

Gustav is also likely to strike New Orleans, the U.S. city devastated by Hurricane Katrina three years ago, as early as Monday.

New Orleans Mayor Ray Nagin has ordered the city to be evacuated.

John McCain, the presumptive Republican presidential nominee, and his running mate Sarah Palin will fly to Mississippi Sunday to check on safety measures in place.

Gustav, the seventh tropical storm of the Atlantic season, has killed at least 86 people in the Dominican Republic, Haiti and Jamaica. Some 59 people were killed and 22 injured in Haiti alone.