Tropical Storm Gordon gained strength as it moved steadily toward the US Gulf Coast Tuesday, on track to make landfall just east of New Orleans with hurricane force winds.

Authorities declared a state of emergency in the "Big Easy" devastated in 2005 by mega Hurricane Katrina -- as well as in Mississippi, and encouraged people living outside its levee system to evacuate voluntarily.

The Miami-based National Hurricane Center (NHC) said Gordon, which formed near the upper Florida Keys Monday, was 75 miles southeast of the coastal city of Biloxi, Mississippi at 0001 GMT (Wednesday).

A hurricane warning was in place from the mouth of the Pearl River, on the Louisiana-Mississippi state line, to the Alabama-Florida border to the east.

Troy Peterson, the sheriff of Mississippi's Harrison County declared a curfew from 7:00pm local time (0001 GMT) until 7am the next day, according to local broadcaster WLOX, while the Mississippi Gaming Commission ordered all casinos to stop operating at 5:00 pm.

Gordon was moving on a northwesterly track at a speed of 14 miles per hour, packing maximum sustained winds of 70 miles per hour (110 kilometers per hour) that extended up to 80 miles from the storm's center.

"On the forecast track, the center of Gordon will make landfall along the north-central Gulf Coast within the hurricane warning area this evening or tonight, and then move inland over the lower Mississippi Valley through Wednesday," the NHC said in a statement.

Up to eight inches of rain could fall across the Gulf states. Meanwhile, warnings of a "life-threatening" storm surge of up to five feet were in place across a stretch of the Louisiana and Alabama coastline east of New Orleans.

"The deepest water will occur along the immediate coast near and to the east of the landfall location, where the surge will be accompanied by large waves," the NHC said.

The NHC added it expects "rapid weakening" once Gordon makes landfall.