Hurricane Isaac crashed ashore in southeast Louisiana on Tuesday, bringing high winds and soaking rains that pose the first test for multibillion-dollar flood defences put in place in New Orleans after hurricane Katrina devastated the U.S. Gulf Coast seven years ago.
Flood-control systems and levees failed when Katrina hit in 2005, leaving parts of the New Orleans underwater. Troops and law enforcement officials have been deployed throughout the city this week to prevent a repeat of the chaos and looting that followed in the days and weeks after Katrina.
Isaac killed at least 23 people and caused significant flooding and damage in Haiti and the Dominican Republic before skirting the southern tip of Florida on Sunday.
The effects of the large, slow-moving storm were felt along the coastlines of Louisiana, Mississippi and Alabama. The storm surge caused flooding in Louisiana and winds gusted to 96 kilometres an hour in New Orleans, the National Hurricane Center said in an advisory.
New Orleans Mayor Mitch Landrieu assured residents "your city is secure," and said emergency services were ready for search and rescue missions. This raised the spectre of Katrina, when Coast Guard helicopters plucked stranded residents from the roofs of their flooded houses.
"We're in the heart of this fight," Landrieu told an evening news conference.
"We are in the hunker-down phase."
About 1,000 U.S. National Guard troops in military vehicles took up positions on the city's mostly deserted streets, brandishing assault rifles to ward off any threat of looting.
Isaac spared Tampa, Florida, where the Republican National Convention began on Monday.
President Barack Obama urged residents to take cover and heed warnings, saying that now was "not the time to tempt fate." He issued emergency declarations for Louisiana and Mississippi earlier this week.
On Tuesday morning, army engineers closed the massive new floodgate at Lake Borgne, east of New Orleans, for the first time. It is largest storm-surge barrier in the world.
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