The oil slick spewed by a ruptured oil rig in the Atlantic is moving fast towards the U.S. shorelines, as experts fear it may spell a major ecological nightmare in the worst oil disaster in the country's history.

The oil spill, which started on April 22, two days after a British Petroleum (BP) oil rig exploded, caught fire and sank, killing 11 workers, has also caused a political fallout in the U.S.

President Barack Obama announced a Sunday morning visit to the stricken region in the Gulf of Mexico, as criticism arose about whether the government and the BP have acted swiftly enough to prevent the disaster.

The ruptured well, some 80 km off the coast, is spewing 200,000 gallons of crude oil into the sea each day.

Researchers said the area of the slick on Friday expanded to about 9,000 square kilometers, similar in size to Puerto Rico, three times bigger than originally estimated.

The rate of the oil spill is also increasing, as is indicated by analysis of images collected from satellites. Inopportune southeasterly winds further complicated the situation by driving the slick faster towards the U.S. coastline.

The total amount of oil spill in the sea now remains disputed, but even at the current rate of leakage, the spill should surpass the 1989 EXXon Valdez incident as the worst U.S. oil disaster in history within about a week, experts agree.

The slick spells a major ecological nightmare for the U.S. Gulf Coast shoreline, one of the nation's most abundant sources of sea lives including fish, shrimp, crabs, oysters and others.

The governor of Louisiana, the state at the forefront of this catastrophe, on Saturday said the oil "literally threatens our way of life." The state closed its shrimping grounds and oyster beds and declared a state of emergency, together with the states of Forida, Alabama and Mississippi.