The outer edge of Hurricane Gustav reached the US Gulf of Mexico coast early on Monday, with rain and tropical storm force winds beginning to lash New Orleans, a US National Hurricane Center official said.
"The outer edge of the storm is already over the Mississippi Delta and going in toward New Orleans now, according to radar," center meteorologist Patricia Wallace told AFP.
Nearly two million people have fled the state of Louisiana ahead of the hurricane in what is being called the largest evacuation in US history, and officials have shut down the area's vital oil production facilities.
Reports of power outages in eastern portions of New Orleans began after wind and rain began hitting the city late Sunday.
However, Gustav's eye was not expected to make landfall until early afternoon on Monday.
At 0300 GMT, the eye was located 220 miles (360 kilometers) southeast of New Orleans and moving northwest at 16 miles (26 kilometers) an hour.
However, the hurricane had a wide swing, with tropical storm force winds extending as far as 220 miles (350 kilometers) outward, the center said in its advisory.
Still a category three hurricane, Gustav packed sustained winds of 115 miles (185 kilometers) per hour.
Forecasters predicted a slight strengthening before landfall, but Gustav was expected to stay at category three for the rest of its journey across of the Gulf of Mexico.