Extraordinary footage has emerged from inside the eye of Hurricane Ida as it hit Louisiana, lashing the coast with 240km/h winds, torrential downpours and pounding surf that plunged the shoreline under metres of water.

The US’s National Hurricane Centre shared the astonishing video taken by storm researchers deep inside the extremely dangerous category four storm as it made landfall on Sunday (local time).

There was also footage from the Hurricane Hunters, a branch of the US Air Force Reserve.

“Those impacted are in our thoughts. And shoutout to everyone on the ground ready to respond once the storm passes,” the Hunters wrote on Twitter.

Tweet from @NHC_Atlantic

Hurricane Ida – one of the most devastating storms to hit the US – ploughed through the Gulf of Mexico into Louisiana, lashing the state 16 years to the day after Hurricane Katrina made landfall, triggering devastating floods.

Ida knocked out power to all of New Orleans, blew roofs off buildings and reversed the flow of the Mississippi River.

“This is going to be much stronger than we usually see and, quite frankly, if you had to draw up the worst possible path for a hurricane in Louisiana, it would be something very, very close to what we’re seeing,” state Governor John Bel Edwards said.

Residents in Louisiana woke up to a monster storm after Ida’s top recorded winds grew by 72km/h in five hours, as the hurricane moved through some of the warmest ocean water in the world, in the northern Gulf of Mexico.

With communities in the most vulnerable coastal areas ordered to evacuate in advance, residents riding out the storm in their homes braced on Sunday for the toughest test yet of major upgrades to a levee system constructed following devastation of Katrina.

Mr Edwards voiced confidence in the billions of dollars in levee improvements since then, saying they were “built for this moment.”

Tweet from @53rdWRS

Less than 160 kilometres inland to the north, flash-flood warnings were issued for downtown New Orleans, where emergency medical services were suspended earlier in the day. New Orleans is the biggest city in a state already reeling from a fourth wave of COVID-19 infections and hospitalisations.

Officials of the US Army Corps of Engineers said they expected the city’s newly-reinforced levees to hold, though they said the flood walls could be overtopped in some places.

Power outages were widespread in the first hours of the storm, with more than 530,000 Louisiana homes and businesses losing electricity by late in the day, according to state utility Entergy Louisiana.

“As soon the storm passes, we’re going to put the country’s full might behind the rescue and recovery,” President Joe Biden said after a briefing at the headquarters of the Federal Emergency Management Agency in Washington.

Mr Biden earlier said 500 federal emergency response workers were posted in Texas and Louisiana to respond to the storm.

Inundation from Ida’s storm surge – high surf driven by the hurricane’s winds – was reported to have exceeded predicted levels of 1.83 metres along parts of the coast.

The NHC also warned of potentially catastrophic wind damage and up to 60 centimetres of rain in some areas.

Officials had ordered widespread evacuations of low-lying and coastal areas, jamming highways and depleting petrol supplies as residents and vacationers fled, although Mr Edwards said it was impossible to evacuate hospitals.

Louisiana hospitals were treating about 2450 COVID-19 patients after the latest surge of infections, Mr Edwards said, with many already nearing capacity.

The Bureau of Safety and Environmental Enforcement said nearly 300 offshore oil and gas platforms were evacuated, cutting Gulf-based petroleum and natural gas production by 96 per cent and 94 per cent, respectively.

-with AAP