People watch the waves kicked up by Hurricane Ida in the resort area of Cancun, Mexico, on Sunday. (Israel Leal/Associated Press)

A hurricane warning was issued for the northern U.S. Gulf Coast on Sunday night as Hurricane Ida churned across the Gulf of Mexico with winds of 165 kilometres an hour.

The warning extends from the Mississippi-Alabama border eastward to Indian Pass, Fla., and means that hurricane conditions are expected within 24 hours.

A tropical storm warning and a hurricane watch were issued for parts of Louisiana, including New Orleans and Lake Pontchartrain, eastward to Alabama.

At 10 p.m. ET, the Category 2 hurricane was centred about 645 kilometres south-southeast of the mouth of the Mississippi River and was expected to cross the Gulf of Mexico overnight and Monday.

Forecasters at the U.S. National Hurricane Center in Miami said gradual weakening is expected, but Ida is expected to remain a hurricane as it approaches the northern Gulf Coast.

On its current path, the hurricane is forecast to brush Louisiana and Mississippi before making landfall near Alabama and continuing across north Florida.

Louisiana Gov. Bobby Jindal declared a state of emergency Sunday as a precaution and the National Guard was on high alert. New Orleans wasn't included in the hurricane watch.

Mississippi authorities warned residents to be vigilant and said they were monitoring conditions to see whether any evacuations of lower-lying areas or school closures would be necessary.

Mississippi Emergency Management Agency director Mike Womack said forecasts called for tides of 1.2 metres to 2.1 metres above normal and rainfall totals of up to 180 millimetres within 24 hours, which could mean flooding along the coasts and rivers.

In the Florida Panhandle, residents in Bay County and Panama City were advised to secure boats and prepare for storm surges that could reach a metre.

Earlier Sunday, Ida's wind and rain lashed the Mexican resort city of Cancun, where tour operators and fishermen pulled their boats out of the water.

All hurricane watches and warnings were cancelled for Mexico by Sunday evening. A tropical storm warning remained in effect for the Cuban province of Pinar del Rio.

In El Salvador, at least 124 people have died from flooding following three days of heavy rains that may be indirectly tied to Ida.

Dave Roberts, a U.S. navy hurricane specialist at the U.S. National Hurricane Center, said Ida's presence in the Caribbean may have played a role in drawing a Pacific low pressure system toward El Salvador, causing those rains.

However, he said, "if there were deaths associated with this rainfall amount in El Salvador, I would not link it to Ida."

Hurricane Ida passed through El Salvador's neighbour Nicaragua on Thursday, damaging or destroying about 500 homes, as well as roads, bridges and public buildings.

With files from The Associated Press