A powerful storm has made landfall in Texas as a Category 4 hurricane in what officials have warned could be a "major disaster" for the US state and surrounding areas.
The eye of Hurricane Harvey hit land between the Port of Aransas and Port O'Connor, Texas late on Friday, according to the National Hurricane Center.
It is expected to be the most powerful hurricane to hit the US mainland since 2005.
Prior to the storm making landfall, US President Donald Trump signed a disaster proclamation for Texas, freeing up federal funds for assistance.
Earlier in the day, Texas Governor Greg Abbott had asked Trump to preemptively declare Harvey a "major disaster" in order to speed federal aid.
"We can obviously tell already at this stage this is going to be a very major disaster," Abbot said, as more than 1,000 National Guardsmen were activated.
"We're going to be dealing with really record-setting flooding in multiple regions."
|This enhanced satellite image shows Hurricane Harvey, middle left, approaching the coast of Texas on Friday [NASA/NOAA via AP]|
Al Jazeera's Allen Schauffler, reporting from Victoria, Texas, said: "Some of the smaller communties up the Gulf coast of Texas are now really bearing the brunt of the storm surge and the high winds."
Category 4 winds can top 230km per hour.
"It's really an extraordinary and dangerous storm," Schauffler said.
Motorways leading from coastal areas were jammed as authorities issued urgent warnings to hundreds of thousands of residents to flee. Some motorways were to be turned into one-way roads to speed the exodus from the storm zone.
There were also reports of massive power outages as the storm approached Texas' coast.
Harvey, the first major storm of the annual Atlantic hurricane season, was packing maximum sustained winds of 195km per hour.
The storm is expected to dump up to 89cm of rain over a four or five-day period in parts of Texas.
Major test for Trump
Satellite images showed the massive storm system extending hundreds of kilometres into the Gulf of Mexico.
It is forecast to be the most powerful hurricane to hit the mainland since Wilma struck Florida in 2005, and could inflict billions of dollars in damage.
The arrival of Harvey is likely to be a major test for the Trump, who the White House said would head to the affected region early next week.
Officials said Trump was being briefed regularly on the storm and had spoken to Texas and Louisiana governors.
"I encourage everyone in the path of #HurricaneHarvey to heed the advice & orders of their local and state officials," Trump tweeted on Friday.
"This storm will likely be very destructive for several days," the White House added in a statement.
Before the storm hit, the US Federal Emergency Management Agency (FEMA), prepositioned emergency supplies.
In 2005, Bush faced severe criticism after FEMA appeared unprepared for the devastating damage inflicted by Hurricane Katrina.
"Keep on top of hurricane Harvey don't make same mistake President Bush made with Katrina," Republican Senator Chuck Grassley urged the Trump in a tweet.
FEMA chief Brock Long said the most pressing danger was the storm surge, the high tides powered by powerful winds - expected to reach between 1.8 metres and 3.6 metres in some areas - but said many inland counties should prepare for "significant" flooding.
Al Jazeera's Diane Easterbrook, reporting from Galveston, Texas, said that the storm is "turning out to be much worse than anyone had expected".
She added that just a few days ago, it was "only a minor tropical depression".
Meteorologist Eric Holthaus told AFP news agency that the prospect of the storm stalling on the coast, lashing it with heavy rain for days, "is just terrifying".
"This is the sort of storm that meteorologists prepare for and think about for years," he said.
Coastal Texas is a fast-growing area, with some 1.5 million people moving into the area since 1999.
Authorities said the combination of dense growth and perhaps a year's worth of rain falling in just days could prove deadly.
Local television footage showed supermarket aisles plucked bare, houses and shops with windows boarded over, and long lines snaking outside gas stations.
Those who had evacuated said they were "just trying to get ahead of the storm".
"It has been pretty stressful," Corpus Christi resident Corey Martinez told Reuters news agency at a gas station about 77km north of Houston.
"We're just trying to get ahead of the storm. We've never been through a hurricane before," he said.
David Ramirez, another Corpus Christi resident, left his home early on Friday to wait out the storm in San Antonio, Texas.
"With the level of storm surge they're talking about, there isn't a lot I could do to protect my house," Ramirez said.
Source: Al Jazeera and news agencies