Hurricane Harvey smashed into Texas late Friday, lashing a wide swath of the Gulf Coast with strong winds and torrential rain from the fiercest cyclone to hit the U.S. in more than a decade.

The U.S. National Hurricane Center said the eye of the Category 4 hurricane made landfall about 10 p.m. local time about 48 kilometres northeast of Corpus Christi between Port Aransas and Port O'Connor, bringing with it 209 km/h sustained winds and flooding rains.

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Rain is blown past palm trees as Hurricane Harvey makes landfall in Corpus Christi, Texas. Harvey intensified into a hurricane Thursday and steered for the Texas coast with the potential for almost a metre of rain. (Eric Gay/Associated Press)

Harvey's approach sent tens of thousands of residents fleeing the Gulf Coast, hoping to escape the wrath of an increasingly menacing storm set to slam an area of Texas that includes oil refineries, chemical plants and dangerously flood-prone Houston, the nation's fourth-largest city.

Texas Gov. Greg Abbott warned that the monster system would be "a very major disaster," and the forecasts drew fearful comparisons to Hurricane Katrina, one of the deadliest ever to strike the U.S.

Reports of damage

Reports of damage began to emerge from Rockport, Texas, a coastal city of about 10,000 people that was directly in the path of Harvey when it came ashore.

Rockport City Manager Kevin Carruth said by telephone that he had heard reports of a tree falling into a mobile home and roofs collapsing on houses. The city, about 50 kilometres northeast of Corpus Christi, had peak wind surges of more than 201 km/h, according to the U.S. National Weather Service.

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A damaged stop light blocks a street as Hurricane Harvey makes landfall in Corpus Christi, Texas. (Nick Wagner/Austin American-Statesman via AP)

Volunteer Fire Department Chief Steve Sims said there are about 15 volunteer firefighters at the city's fire station waiting for conditions to improve enough for their vehicles to safely respond to pleas for help.

"There's nothing we can do at this moment. We are anxious to get out there and make assessments, but we're hunkered down for now," he said.

Earlier Friday, Rockport Mayor Pro Tem Patrick Rios offered ominous advice, telling KIII-TV those who chose to stay put "should make some type of preparation to mark their arm with a Sharpie pen," implying doing so would make it easier for rescuers to identify them.

In Corpus Christi, the major city closest to the centre of the storm, wind whipped palm trees and stinging sheets of horizontal rain slapped against hotels and office buildings along the city's seawall as the storm made landfall. Boats bobbed violently in the marina. It was too dark to tell whether any boats had broken their moorings.

Fuelled by warm Gulf of Mexico waters, Harvey grew rapidly, accelerating from a Category 1 early in the morning to a Category 4 by evening. Its transformation from an unnamed storm to a life-threatening behemoth took only 56 hours, an incredibly fast intensification.

Harvey came ashore as the fiercest hurricane to hit the U.S. in 13 years and the strongest to strike Texas since 1961's Hurricane Carla, the most powerful Texas hurricane on record. Based on the atmospheric pressure, Harvey ties for the 18th strongest hurricane on landfall in the U.S. since 1851 and ninth strongest in Texas.

91 cm of rain

Aside from the winds of 209 km/h and storm surges up to four metres, Harvey was expected to drop up to 91 centimetres of rain. The resulting flooding, one expert said, could be "the depths of which we've never seen."

Galveston-based storm surge expert Hal Needham of the private firm Marine Weather and Climate said forecasts indicated that it was "becoming more and more likely that something really bad is going to happen."

At least one researcher predicted heavy damage that would linger for months or longer.

"In terms of economic impact, Harvey will probably be on par with Hurricane Katrina," said University of Miami senior hurricane researcher Brian McNoldy. "The Houston area and Corpus Christi are going to be a mess for a long time."

Hundreds of medical professionals called in

Before the storm arrived, home and business owners nailed plywood over windows and filled sandbags. Steady traffic filled the highways leaving Corpus Christi, but there were no apparent jams. In Houston, where mass evacuations can include changing major highways to a one-way vehicle flow, authorities left traffic patterns unchanged.

Federal health officials called in more than 400 doctors, nurses and other medical professionals from around the nation and planned to move two 250-bed medical units to Baton Rouge, La. Other federal medical units are available in Dallas.

Hurricane Harvey's path

Just hours before the projected landfall, the governor and Houston leaders issued conflicting statements on evacuation.

After Abbott urged more people to flee, Houston authorities urged people to remain in their homes and recommended no widespread evacuations. 

Flooding a danger in Houston

In a Friday news conference that addressed Houston officials' decision to not have a voluntary or mandatory evacuation, Houston Mayor Sylvester Turner said there might be a "greater danger" in having people who don't need to be evacuated on roads that could flood.

Harris County Judge Ed Emmett said that because the hurricane was not taking direct aim at Houston, the city's primary concern was heavy flooding.

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Guadalupe Guerra rests her head on the shoulder of her husband, Ray, while waiting to board a bus at an evacuation center in Corpus Christi, Texas. Hundreds of residents of the Corpus Christi area boarded buses Friday to be transported to a shelter in San Antonio. (Nick Wagner/Austin American-Statesman via AP)

"We are not having a hurricane," said Emmett, the top elected official for the county, which encompasses Houston. "We are having a rain event."

At a convenience store in Houston's Meyerland neighbourhood, at least 12 cars lined up for fuel. Brent Borgstedte said this was the fourth gas station he had visited to try to fill up his son's car. The 55-year-old insurance agent shrugged off Harvey's risks.

Major effects possible well inland

"I don't think anybody is really that worried about it. I've lived here my whole life," he said. "I've been through several hurricanes."

Scientists warned that Harvey could become powerful enough to swamp counties more than 161 kilometres inland and stir up dangerous surf as far away as Alabama and the Florida Panhandle, 1,126 kilometres from the projected landfall.

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A power generator tips in in front of Texas's CHRISTUS Spohn Hospital as Hurricane Harvey approaches. (Courtney Sacco/Corpus Christi Caller-Times via AP)

It may also spawn tornadoes. Even after weakening, the system might spin out into the Gulf and regain strength before hitting Houston a second time Wednesday as a tropical storm, forecasters said.

All seven Texas counties on the coast from Corpus Christi to the western end of Galveston Island ordered mandatory evacuations from low-lying areas. Four counties ordered full evacuations and warned there was no guarantee of rescue for people staying behind.

Voluntary evacuations have been urged for Corpus Christi and for the Bolivar Peninsula, a sand spit near Galveston where many homes were washed away by the storm surge of Hurricane Ike in 2008.

Tropical Weather

Caesar Mendez and his daughter Catalina wait inside the Corpus Christi Natatorium to board a bus to evacuate to San Antonio ahead of Hurricane Harvey on Thursday. (Courtney Sacco/Corpus Christi Caller-Times/Associated Press)

Trump's first test

State officials said they had no count on how many people actually left their homes.

Space and ocean agencies release satellite images of hurricane0:34

The storm posed the first major emergency management test of U.S. President Donald Trump's administration.

The White House said Trump was closely monitoring the hurricane and planned to travel to Texas early next week to view recovery efforts. The president was expected to receive briefings during the weekend at Camp David, and signed a federal disaster declaration for six coastal counties Friday night.