A teenage girl is among four people killed in separate incidents of trees falling and crushing their homes during the strongest hurricane to hit Louisiana in more than 160 years.

Hurricane Laura barrelled through southwest Louisiana, destroying buildings in the city of Lake Charles and killing a 14-year-old girl after making landfall at Category 4 strength.

“It looks like 1,000 tornadoes went through here. It’s just destruction everywhere,” Brett Geymann, who was among thousands of residents to evacuate the state, told USA TODAY.

At least three more people have been reported to have died after trees fell on their homes in Louisiana.

They include a 60-year-old in Acadia Parish and two others in Jackson and Vernon parishes.

Meanwhile, a chemical plant in the middle of southwest Louisiana caught fire, sending thick smoke containing poisonous chlorine billowing into the air.

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All residents have been urged to stay indoors, turn off air conditioning units and to wait for further directions from local officials.

Residents of Lake Charles heard Laura’s winds howling and the sound of breaking glass as the storm passed through the city of 78,000 with winds of 137 km per hour and gusts up to 206 kph in the hour after landfall.

The windows of the city’s 22-floor Capital One Tower were blown out, street signs were toppled and pieces of wooden fence and debris from collapsed buildings lay scattered in the streets, video footage showed.

Laura is considered the strongest hurricane to hit Louisiana since 1856.

Lake Charles resident Borden Wilson, a 33-year-old pediatrician, was anxiously anticipating his return home after evacuating to Minden, Louisiana.

“I never even boarded up my windows. I didn’t think to do that. This is the first hurricane I’ve experienced. I just hope my house is fine,” he told Reuters.

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About 620,000 people were under mandatory evacuation orders in Louisiana and Texas – but not everyone fled from the area.

“There are some people still in town, and people are calling … but there ain’t no way to get to them,” Tony Guillory, president of the Calcasieu Parish Police Jury said.

Officials across the hard-hit area said it would be several hours before they could get out to begin search and rescue missions.

Downed trees blocking roadways were expected to be the biggest immediate challenge for rescuers.

“We know anyone that stayed that close to the coast, we’ve got to pray for them, because looking at the storm surge, there would be little chance of survival,” Louisiana Lieutenant Governor Billy Nungesser told ABC’s Good Morning America.

The hurricane hit with powerful winds causing extensive damage to the city. Photo: Getty

Laura made landfall just before 1am on Thursday local time as a Category 4 storm packing winds of 240 kph in the small town of Cameron, Louisiana, the National Hurricane Center said.

It rapidly weakened to a Category 2 storm on Thursday morning with maximum sustained winds of 160 kph before becoming a tropical storm later in the day.

Hurricane Laura didn’t bring “the absolute catastrophic damage that we thought that was likely”, but “a tremendous amount of damage” has been sustained, Louisiana Governor John Bel Edwards told reporters.

The National Weather Service’s latest forecast advisory is of “flooding rainfall and strong winds spreading inland over northern Louisiana and southeastern Arkansas”.

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It’s expected the clean-up in the worst affected areas will take weeks or months. Meanwhile, about 750,000 people are without power in Louisiana and Texas.

 A Confederate general fell victim to Hurricane Laura.

The South’s Defenders monument has stood since 1915 outside a US courthouse in Lake Charles, Louisiana, where local authorities voted 10-4 this month to keep it in place.

Critics call it a symbol of racism that glorifies slavery.

But a Calcasieu Parish official said when they asked for public commentsm they received 878 written responses against relocating the monument and only 67 in favour of moving it.

A statue of a Confederate soldier in front of a courthouse in Lake Charles after being toppled when Hurricane Laura ripped through the area. Photo: AAP

Now the pedestal is empty and the Confederate statue is in pieces on the ground, victim to a Category 4 hurricane that struck the city early on Thursday.

President Donald Trump said he will visit Louisiana and Texas this weekend to survey the damage.

He said he considered pushing back his speech to the Republican National Convention but “it turned out we got a little bit lucky”.

Laura “was very big, it was very powerful but it passed quickly. And so everything is going to be on schedule,” he said.

-with AAP