Louisiana officials have ordered people along the Tangipahoa River between the towns of Kentwood and Robert to evacuate due to the expected failure of a dam in Mississippi that was damaged by Tropical Storm Isaac.

Up to 60,0000 people in Louisiana downstream of the Lake Tangipahoa Dam near McComb, Mississippi, have been ordered to leave.

The dam, located in Percy Quinn State Park, is about 161km north of New Orleans, which is not in danger.

The dam was badly damaged in the storm but "has not been breached at this time," said Carlene Statham, deputy director of civil defence in Pike County, Mississippi.

Mississippi officials are planning to intentionally breach it to prevent a failure, Jindal said, calling the situation at the dam "very fluid." If the dam is intentionally breached it would not impact Louisiana, he said.

Officials have ordered residents 1.6km on either side of the river to evacuate, and Jindal has ordered buses to the area to help residents leave, Tangipahoa Parish President Gordon Burgess said.

A National Guard helicopter is in the air monitoring the dam, Jindal said. If the dam fails, it would take about 90 minutes for the water to reach Kentwood, he said.

Jindal said he planned to survey the dam with Burgess by air later today.

Meanwhile, search-and-rescue operations around New Orleans resumed after Hurricane Isaac brought heavy flooding.

Relieved residents and authorities said the storm's destruction was nothing like that seen from Hurricane Katrina in 2005.

Isaac, a slow-moving Category One hurricane when it hit the region on Tuesday, was expected to weaken into a tropical depression today.

However, it could still bring heavy rain and floods as it moves over the central US, where rain is badly needed, in the next few days.

More than 730,000 residents of Louisiana and Mississippi were without power.