The mayor of New Orleans has called on residents to evacuate unprotected city neighbourhoods as Hurricane Ida bears down on the Louisiana coastline.

“What I am told is that this storm will not be weakening,” Mayor LaToya Cantrell said on Saturday.

Hurricane Ida has intensified over the warm waters of the Gulf of Mexico ahead of its expected arrival on the southern US coast on Sunday.

It has already brought heavy rain and high winds to western Cuba.

A mandatory evacuation is in place for some parts of New Orleans – those outside the levees – while the rest of the city has been issued with a voluntary evacuation order.

The levees are a system of flood walls, built to protect low-lying New Orleans, and strengthened after Hurricane Katrina in 2005.

“If you’re going to leave you need to do that now,” Ms Cantrell said. “We need to make sure you are in a safe place. Everyone, whether you are going to leave voluntarily or stay on site, hunker down.”

She added that anyone unable to leave the city should “prepare for damaging wind, power outages, heavy rain, tornadoes”.

The impact of climate change on the frequency of storms is still unclear, but increased sea surface temperatures warm the air above and make more energy available to drive hurricanes, cyclones and typhoons. As a result, they are likely to be more intense with more extreme rainfall. 

Forecasters say the hurricane will be at category 4 strength by the time it reaches the northern coast of the Gulf of Mexico.

More than 80 oil rigs in the Gulf of Mexico have been evacuated and half the region’s oil and gas output has been suspended.

Ida passed over western Cuba on Friday, hitting the Isle of Youth with maximum sustained winds of 75mph (120km/h).

Coincidentally, Sunday marks the 16th anniversary of Hurricane Katrina, which devastated New Orleans after making landfall as a category 3. Katrina flooded 80% of the city and killed more than 1,800 people.

Experts say that if storm surges hit at a time that coincides with high tides, sea water could flood over the New Orleans levee system and into the city.

Governor Bel Edwards has declared a state of emergency and called for anyone along the state’s coastline to shelter in place starting on Saturday evening.

President Joe Biden said on Saturday that Ida was “turning into a very, very dangerous storm” and the federal government was ready to provide help.